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ECONOMIC  GEOLOGY 


BY 

CHARLES  H.  RICHARDSON 

PROFESSOR  OP  MINERALOGY' 'AND  ECONOMIC  GEOLOGY, 
SYRACUSE  UNIVERSITY,  NEW  YORK 


McGRAW-HILL  BOOK  COMPANY,  INC. 
239  WEST  39TH  STREET,  NEW  YORK 

6  BOUVERIE  STREET,  LONDON,  E.  C. 

1913 


K-3 


COPYRIGHT,  1913,  BY  THE 
MCGKAW-HILL  BOOK  COMPANY,  INC. 


o 


THE. MAPLE. PKE88.TORK. PA 


PREFACE 

This  work  is  based  upon  a  series  of  lectures  which  the  author 
has  been  compiling  for  more  than  twenty  years.  It  treats  only 
of  the  metallic  ores  in  addition  to  the  chapters  on  the  origin  of  ore 
deposits.  The  metals  are  arranged,  with  the  exception  of  the 
precious  and  rare  metals,  in  the  order  of  their  group  separation, 
and  the  chapters  comprise  the  metals  of  the  different  groups. 
A  final  chapter  gives  the  economic  or  statistical  treatment. 

It  has  seemed  wise  to  the  author  to  omit  the  references  which 
are  given  to  students  for  library  or  laboratory  work,  as  these  are 
best  worked  out  by  each  teacher  to  meet  his  own  views  and  the 
needs  of  his  individual  pupils.  The  author  has  in  preparation 
also  a  companion  book  covering  the  non-metallics. 

The  author  wishes  to  express  his  great  indebtedness  to  Prof. 
T.  C.  Hopkins,  Syracuse  University,  who  has  read  both  the 
manuscript  and  the  galley  proofs  and  offered  many  timely  sug- 
gestions in  the  preparation  of  the  book;  to  Prof.  W.  J.  Miller, 
Hamilton  College,  who  has  read  the  manuscript  entire;  to  the 
many  professors  of  other  universities  who  have  read  various 
chapters  of  the  manuscript  and  heartily  cooperated  with  the 
author  in  this  work;  to  Prof.  Heinrich  Ries,  Cornell  University, 
not  only  for  his  " Economic  Geology,"  but  also  for  the  use  of 
many  of  his  photographs  to  which  credit  is  given  in  the  text;  to 
Thomas  and  MacAlister,  authors  of  "The  Geology  of  Ore 
Deposits";  to  F.  W.  Clarke,  Chief  Chemist  of  the  U.  S.  Geological 
Survey,  "The  Data  of  Geochemistry";  to  Prof.  J.  F.  Kemp, 
Columbia  University,  "Ore  Deposits  of  the  United  States  and 
Canada";  to  Prof.  J.  C.  Branner,  Leland  Stanford  University, 
"Syllabus  of  Economic  Geology";  to  the  authors  of  the  Mineral 
Industry,  its  Statistics,  Technology  and  Trade;  to  the  compilers 
of  the  various  volumes  of  the  Mineral  Resources;  to  the  authors 
of  all  geological  publications  whose  works  have  been  consulted 
and  embodied  in  part  in  this  volume;  to  the  Macmillan  Company 
for  their  courtesy  in  loaning  many  cuts;  to  the  Engineering  and 
Mining  Journal  and  the  Canadian  Geological  Survey  for  the  use 
of  illustrations;  and  to  the  authors  of  all  other  cuts  save  the 
original  drawings  from  whatsoever  source  they  may  have  been 
derived. 

CHARLES  H.  RICHARDSON. 

SYRACUSE  UNIVERSITY, 
November,  1913. 


TABLE  OF  CONTENTS 

CHAPTER  I 

PAGES 

ORE  DEPOSITS — INTRODUCTION 1-23 

Definition,  1.  Primary  source  of  ores,  1-2.  Enrichment  of 
ore  bodies,  3.  Causes  of  precipitation,  4.  Mineral  springs,  6. 
Origin  of  cavities,  7.  Faults,  9.  Veins,  11.  Richness  of 
veins,  14.  Irregularities  in  veins,  14.  Ribbon  structure,  15. 
Age  of  veins,  18.  Classification  of  ore  deposits,  18-20. 
What  constitutes  a  mine?,  20-23. 

CHAPTER  II 

ORIGIN  OF  ORE  DEPOSITS 24-51 

Meteoric  origin,  24.  Number  of  meteorites,  24.  Content  of 
meteorites,  25.  Segregation,  25-29.  Pneumatolysis,  29-33. 
Hydatogenesis,  33-35.  Metasomasis,  35-41.  Precipitation, 
41-42.  Metamorphism,  42-46.  Secondary  changes,  46-47. 
Detrital  deposits,  47-51. 

CHAPTER  III 

PRECIOUS  METALS — GOLD,  SILVER,  PLATINUM 52-109 

Ores  of  gold,  52.  Character  of  the  ore  bodies,  56.  Geograph- 
ical distribution,  60-83.  Appalachian  belt,  60.  Black  Hills 
district,  62.  Cordilleran  region,  66.  Sierra  region,  72. 
Pacific  Coast  region,  75.  Alaskan  field,  77.  Placers,  79. 
Placers  classified,  81.  Porcupine,  83.  Geological  horizon,  83. 
Placer  mining,  84.  Methods  of  extraction,  86-89.  Uses,  89. 
Silver,  89.  Character  of  the  ore  bodies,  91-97.  Geographical 
distribution,  97.  Geological  horizon,  98.  Methods  of  extrac- 
tion, 98-102.  Uses,  102.  Platinum,  102.  Methods  of  extrac- 
tion, 104.  Uses,  104.  Rare  precious  metals,  106-108.  Losses 
of  the  precious  metals,  108-109. 

CHAPTER  IV 

USEFUL  METALS  (GROUP  I) 

LEAD,  MERCURY 110-130 

Ores  of  lead,  110.  Origin  of  the  ores,  111.  Character  of  the 
ore  bodies,  111-114.  Geographical  distribution,  114-122. 
Appalachian  district,  114.  Mississippi  River  belt,  115. 
Cordilleran  district,  117.  Geological  horizon,  122.  Methods 
of  extraction,  122-123.  Uses,  123-126.  Ores  of  mercury,  126. 

vii 


viii  TABLE  OF  CONTENTS 

PAGES 

Origin  of  ores,  126.  Character  of  ore  bodies,  127.  Geo- 
graphical distribution,  128.  Geological  horizon,  129. 
Methods  of  extraction,  129.  Uses,  130. 

CHAPTER  V 
USEFUL  METALS  CONTINUED  (GROUP  II,  SUBGROUP  A) 

BISMUTH,  COPPER,  CADMIUM 131-163 

Ores  of  bismuth,  131.  Origin  of  the  ores,  131.  Character  of 
the  ore  bodies,  132.  Geographical  distribution,  132. 
Methods  of  extraction,  133.  Uses,  133.  Ores  of  copper,  135. 
Origin  of  the  ores,  135-138.  Classification  of  the  origin  of 
copper  ores,  138.  Character  of  the  ore  bodies,  139.  Geo- 
graphical distribution,  140-157.  The  Appalachian  belt,  140. 
Lake  Superior  region,  142.  The  Cordilleran  section,  145. 
Arizona,  150.  The  Pacific  Coast  belt,  153.  Bingham,  Utah, 
154.  The  Alaskan  district,  155.  Geological  horizon,  157. 
Methods  of  extraction,  157-159.  Uses,  159.  Cadmium, 
160-163. 

CHAPTER  VI 
USEFUL  METALS  CONTINUED  (GROUP  II,  SUBGROUP  B) 

ARSENIC,  ANTIMONY,  TIN 164-187 

Ores  of  arsenic,  164.  Origin  of  the  ores,  164.  Geographical 
distribution,  165.  Methods  of  extraction,  167.  Uses,  168. 
Ores  of  antimony,  171.  Origin  of  the  ores,  171.  Geographical 
distribution,  172.  Methods  of  extraction,  173.  Uses,  174. 
Tin,  176.  Ores  of  tin,  177.  Geographical  distribution, 
179-184.  The  Appalachian  belt,  179.  The  Black  Hills  dis- 
trict, 180.  The  Cordilleran  section,  180.  The  Pacific  Coast 
belt,  180.  The  Alaskan  belt,  181.  Foreign  countries,  181. 
Methods  of  extraction,  184.  Uses,  185. 

CHAPTER  VII 

USEFUL  METALS  CONTINUED  (GROUP  III) 

IRON,  ALUMINUM,  CHROMIUM 188-234 

Ores  of  iron  and  iron  minerals,  188-189.  Origin  of  iron 
minerals,  190-194.  Character  of  the  ore  bodies,  195.  Impur- 
ities that  injure  iron,  196.  Geographical  distribution, 
196-215.  The  Appalachian  district,  196.  Metasomatic 
replacement  deposits,  201.  Residual  limonites,  202.  Gossan 
limonites,  204.  Lake  Superior  district,  204-210.  The  Cor- 
dilleran section,  210.  Hanover,  New  Mexico,  212.  Geo- 
logical horizon,  215.  Methods  of  extraction,  215.  Uses,  216. 
Ores  of  aluminum,  218.  Origin  of  ores,  219.  Character  of 
ore  bodies,  221.  Geographical  distribution,  222.  Methods  of 
extraction,  225.  Uses,  225.  Chromium,  230-234. 


TABLE  OF  CONTENTS  ix 

CHAPTER  VIII 

USEFUL  METALS  CONTINUED  (GROUP  IV) 

PAGES 

COBALT,  NICKEL,  MANGANESE,  ZINC 235-267 

Ores  of  cobalt,  235.  Origin  of  the  ores,  235.  Geographical 
distribution,  236.  Uses,  237.  Ores  of  nickel,  238.  Origin 
of  the  ores,  238.  Character  of  the  ore  bodies,  241 .  Geograph- 
ical distribution,  242.  Sudbury,  Ontario,  242.  Uses,  244. 
Manganese,  245.  Ores  of  manganese,  246.  Origin  of  the 
ores,  246.  Character  of  the  ore  bodies,  248.  Geographical 
distribution,  250.  Cuba,  252.  Uses,  254.  Zinc,  256.  Ores 
of  zinc,  257.  Origin  of  the  ores,  257.  Character  of  the  ore 
bodies,  259.  Geographical  distribution,  259-264.  The  Ap- 
palachian belt,  259.  The  Central  States,  260.  The  Cordil- 
leran  region,  263.  Geological  horizon,  264.  Methods  of 
extraction,  265.  Uses,  266. 

CHAPTER  IX 
THE  RARE  METALS 

MOLYBDENUM,    TUNGSTEN,    TITANIUM,    ZIRCONIUM,    VANADIUM, 

URANIUM,  COLUMBIUM,  TANTALUM,  SELENIUM,  TELLURIUM    .  268-286 
Molybdenum,  268-269.       Tungsten,  269-271.       Titanium, 
271-274.     Zirconium,  274-276.    Vanadium,  276-278.     Uran- 
ium, 278-281.     Columbium,  281.     Tantalum,  282-283.     Sele- 
nium, 283-284.     TeUurium,  285-286. 

CHAPTER  X 

ECONOMICS 287-309 

Gold,  287.  Imports  and  exports,  288.  Silver,  289.  Imports 
and  exports,  290.  Platinum,  291.  Lead,  292.  Mercury,  293. 
Bismuth,  294.  Copper,  295.  Cadmium,  296.  Arsenic,  297. 
Antimony,  297.  Tin,  298.  Iron,  299.  Imports  and  exports, 
300.  Aluminum,  301.  Chrome  iron  ore,  301.  Cobalt,  302. 
Nickel,  302.  Manganese,  303.  Zinc,  304.  Rare  metals,  305- 
309. 

INDEX .   311-320 


ECONOMIC  GEOLOGY 

CHAPTER  I 
ORE  DEPOSITS 
INTRODUCTION 

What  constitutes  an  ore  deposit?  An  ore  deposit  may  be  de- 
fined as  a  body  of  rock  which  contains  metals  or  metallic  com- 
pounds in  sufficient  quantity  to  allow  the  profitable  extraction 
of  some  metallic  content.  A  few  of  the  metals  occur  in  the  native 
state.  This  is  especially  true  of  the  precious  metals:  gold,  silver 
and  platinum.  The  most  common  occurrence  of  the  commercial 
metals  is  that  of  the  sulphides,  oxides/hydrous  oxides,  carbonates, 
etc.  Some  mineral  deposits  which  to-day  do  not  fall  within  the 
definition  of  an  ore  deposit,  may  by  subsequent  concentration 
become  sufficiently  enriched  to  be  of  economic  importance. 

Associated  with  the  metallic  minerals  are  certain  non-metallic 
minerals.  The  commonest  of  these  is  quartz,  Si02;  next  in  the 
order  of  importance  is  calcite,  CaC03,  then  fluorite,  CaF2,  barite, 
BaS04,  and  siderite,  FeC03.  Of  less  importance  than  the  five 
minerals  mentioned  there  appears  as  gangue  minerals  dolomite, 
rhodochrosite,  feldspars,  amphiboles,  pyroxenes,  etc.  It  often 
occurs  that  a  large  part  of  the  vein  consists  of  gangue  and  the  eco- 
nomic product  occupies  the  position  of  a  thin  seam  within  the 
vein-filling. 

These  gangue  minerals  are  of  lower  specific  gravity  than  the  ores 
and  may  often  be  mechanically  separated  from  them .  Again  they 
are  so  barren  of  metallic  minerals  as  to  permit  separation  through 
the  hand  sorting  of  the  ore.  The  gangue  is  then  transported  to 
the  dump,  while  the  material  containing  the  valuable  metal  is 
carried  to  the  mill  for  treatment. 

Primary  Source  of  Ores. — The  question  naturally  arises,  what  is 
the  primary  origin  of  the  ores?  Four  principles  are  cited  by 
C.  R.  Keyes,  in  his  "  Ultimate  Source  of  Ores:"  (1)  Deposition  from 
sea  water.  (2)  Inclusions  of  metallic  minerals  as  accessories  in 

1 


2  ECONOMIC  GEOLOGY 

the  igneous  rocks  and  the  subsequent  extraction,  segregation  and 
cone  entration  of  4ne  ore  materials  through  weathering  processes. 
(3)  Production  of  metalliferous  bodies  in  connection  with  rock 
.masses  ?n  n  molten  state,  either  through  magmatic  segregation  or 
by  the  expulsion  of  the  volatile  compounds  of  the  metals  during 
the  process  of  magma-cooling.  (4)  Derivation  of  metallic  par- 
ticles from  extra-terrestrial  sources,  and  their  later  segregation 
through  the  action  of  surface  water. 

Many  early  writers,  including  the  eminent  chemist  Bischof, 
argued  that  sea  water  was  the  primitive  source  of  the  metallic 
salts  in  nature.  They  claimed  that  the  metallic  salts  of  the 
ocean  were  gathered  into  ore  bodies  where  marine  sediments  were 
laid  down.  The  idea  has  its  foundation  in  the  erroneous  assump- 
tion that  rock  masses  undergo  no  change. 

The  answer  then  to  the  query,  what  is  the  primary  source  of 
the  ores,  is  the  igneous  rocks:  Either  the  deep-seated  masses  upon 
which  the  earliest  sedimentaries  were  deposited,  or  intrusives 
brought  into  the  sedimentaries  in  a  plastic  or  fluid  condition. 

A  certain  amount  of  volcanic  water  is  intimately  associated 
with  the  development  and  enrichment  of  some  ore  deposits 
Even  granites  at  the  time  of  their  formation  contain  much  water, 
which  is  liberated  upon  cooling,  or  when  they  are  brought  near 
the  surface  by  faulting  or  erosion.  The  general  effect  of  mag- 
matic waters  is  reserved  for  discussion  in  the  chapter  on  The 
Origin  of  Ore  Deposits. 

Third,  the  source  from  which  the  water  derives  the  metals  is 
the  zone  of  fracture.  The  jointing  of  limestones,  granites,  and 
basalt  is  familiar.  It  must  be  along  that  line  of  fracture  that  the 
water  seeps,  yet  there  is  a  considerable  amount  of  water  filling 
the  interstices  of  the  rocks  themselves.  The  water  must  gather 
up  the  material  for  transportation  along  these  lines  and  deposit 
it  again  thus  forming  an  ore  body. 

Fourth,  the  force  which  drives  the  water  in  its  circulation  is 
gravity.  This  is  the  recognized  force  that  raises  the  water  in  the 
artesian  well,  that  drives  natural  gas  to  the  dome  where  it  is  found, 
and  petroleum  to  the  pool  where  it  is  collected. 

Three  courses  have  been  advanced  for  the  trend  of  solutions. 
(1)  The  theory  of  the  descensionists.  (2)  The  theory  of  the 
asscensionists.  (3)  The  theory  of  the  lateral  secretionists. 

The  first  theory  that  meteoric  waters  bring  the  minerals  into 
solution  and  carry  them  to  the  lower  depths  has  an  extremely 


ORE  DEPOSITS  3 

limited,  if  indeed,  any  application,  save  in  the  secondary  enrich- 
ment of  ore  bodies.  The  second  theory  is  that  the  solutions  rise 
and  bring  the  materials  for  the  ore  body  from  the  lower  depths 
to  the  higher  altitudes.  If  ore  deposits  are  found  in  the  sedimen- 
tary rocks  as  they  sometimes  are  (with  the  exception  of  the  lead 
and  zinc  deposits  of  Missouri),  the  minerals  were  associated  with 
a  great  rock  mass  whose  detritus  furnished  the  material  for  the 
new  geological  formation.  Again,  the  composition  of  the  igneous 
rocks  as  analyzed  by  the  chemists  of  the  United  States  Geolog- 
ical Survey  leads  to  the  conclusion  that  the  economic  metals  are 
present  in  them  in  minute  quantities,  yet  sufficiently  large,  that 
by  concentration  they  may  become  of  economic  importance. 
Illustration:  gold,  silver,  copper,  lead  and  zinc  have  been  found 
in  fresh  igneous  rocks. 

The  derivation  of  metallic  particles  from  extra- terrestrial  sources 
and  their  later  segregation  through  the  surface  waters  must  also 
be  considered  as  one  of  the  possible  sources  of  certain  classes  of 
ore  deposits.  This  latter  theory  has  thus  far  received  too  little 
attention. 

Enrichment  of  Ore  Bodies. — There  are  four  postulates  relating 
to  the  enrichment  of  ore  deposits  as  follows:  (1)  Ore  deposits 
are  segregated  by  underground  waters.  (2)  The  circulating 
underground  water  is  mainly  of  meteoric  origin.  (3)  The 
source  from  which  the  water  derives  the  metals  is  the  zone  of 
fracture.  (4)  The  force  which  drives  the  water  in  its  circula- 
tion is  gravity. 

The  first  postulate  needs  no  comment.  In  the  second  the 
water  may  be  of  meteoric  or  volcanic  origin.  The  waters  effect- 
ing this  enrichment  are  often  meteoric  and  vadose  for  it  is  that 
body  of  moisture  which  falls  on  the  surface  of  the  earth  that  passes 
through  the  soil  and  along  the  joint  planes  and  through  the  fis- 
sures toward  the  interior  of  the  earth,  and  later  has  a  tendency 
to  appear  again  at  the  surface  of  the  earth  in  seeps  and  fissure 
springs. 

This  may  be  effected  by  infiltration,  by  sublimation  with  steam, 
by  sublimation  with  gas,  or  by  igneous  injection.  The  last  two 
methods  have  a  few  good  applications. 

The  theory  of  the  lateral  secretionist  is  that  the  material 
is  picked  up  along  the  fracture  planes  and  carried  into  the  fis- 
sures by  the  waters  percolating  through  the  rocks  at  right 
angles  to  the  fissure.  These  mineral-bearing  waters  often 


4  ECONOMIC  GEOLOGY 

come  from  a  long  distance  and  derive  the  dissolved  minerals 
from  a  large  amount  of  rock,  but  the  precipitation  occurs  near 
the  surface.  Each  of  the  above  theories  seems  incomplete  in 
itself.  They  supplement  each  other  in  general  harmony  with 
underground  circulation.  The  largest  ore  deposits  like  the 
copper  deposits  of  Michigan  have  sometimes  been  formed  by  a 
single  ascending  solution  and  subsequently  enriched  near  the 
surface  by  descending  solutions;  and  also  both  near  the  surface 
and  at  greater  depths  by  lateral  secreting  solutions. 

The  Causes  of  Precipitation. — Some  authors  have  attributed 
precipitation  to  diminishing  temperature  and  pressure  of  rising 
solutions  alone.  This  is  insufficient.  The  precipitation  is 
generally  due  to  the  mingling  of  different  solutions  in  the  trunk 
channels  whereby  new  chemical  compounds  are  produced. 
Whenever  a  neutral  or  slightly  acid  solution  of  a  lead  salt  comes 
in  contact  with  hydrogen  sulphide  the  lead  is  precipitated  as 
lead  sulphide.  The  resulting  mineral  is  galenite.  Precipita- 
tion is  also  influenced  by  the  character  of  the  wall  rock,  by  the 
infalling  of  fragments  from  the  fissure  walls  and  the  presence 
of  minerals  already  formed.  Replacement  is  also  not  an  infre- 
quent method  of  forming  an  ore  body. 

There  is  a  time-honored  belief  that  ore  bodies  increase  in 
richness  with  depth.  This  theory  is  absolutely  untenable. 
Whether  the  ore  body  will  increase  with  depth  depends  upon 
many  factors;  as  the  breadth  of  the  fissure  at  the  lower  altitudes 
prior  to  the  filling;  the  amount  of  concentration  of  the  ore  that 
has  taken  place  at  the  point  of  the  filling,  and  the  amount  of 
enrichment  that  may  have  occuired  through  faulting  or  the 
introduction  of  intrusive  bodies. 

If  the  upper  unit  of  measurement  is  large  and  there  is  great 
irregularity  in  richness,  the  general  trend  is  toward  impover- 
ishment with  depth.  This  may  arise  from  the  combined  efforts 
of  descending  and  lateral  secreting  solutions  upon  deposits 
already  formed  by  ascending  currents  in  conjunction  with  the 
erosion  of  large  masses  of  overlying  strata.  Occasionally  where 
the  surface  unit  is  large,  there  is  little  decrease  in  width  with 
descent.  This  is  due  to  the  fact  that  the  ore  resulted  from  a 
single  enrichment  by  ascending  waters. 

Gossan. — The  contents  of  the  upper  part  of  the  original  vein 
become  oxidized  in  the  zone  of  weathering,  as  shown  in  Fig.  1, 
and  are  either  washed  away  in  alluvial  deposits  or  are  carried 


ORE  DEPOSITS  5 

down  by  meteoric  waters  to  be  precipitated  by  the  chemical 
action  of  the  underlying  sulphides,  or  the  constituents  of  the 
wall  rock,  or  the  effect  of  ascending  solutions. 

The  surface  illustrations  are  represented  in  the  phenomena, 
known  as  gossan,  or  the  eisener  hut  of  the  German,  or  the  chapeau 
de  fer  of  the  French.  This  is  well  illustrated  in  the  case  of  copper 
mines  where  the  sulphide  of  copper  has  been  dissolved  and  oxi- 
dized to  a  sulphate  and  reprecipitated  at  lower  altitudes  enriching 
the  zone.  The  contact  between  the  oxidized  and  the  unoxi- 
dized  portions  of  the  ore  is  the  richest  part  of  the  entire  vein. 
The  iron  sulphide  becomes  converted  into  an  oxide  or  hydrous 
oxide,  the  reddish  or  yellowish- brown  mineral  so  often  seen  at  the 


FIG.   1. — Superficial  alteration  of  a  contact  deposit.     A,  limestone;  G, 

granite;  0,  ore  body. 

surface.  The  result  of  this  oxidation  and  the  downward  trans- 
ference of  the  copper  is  the  enrichment  of  the  mineral  vein 
for  some  distance.  This  enrichment  varies  with  the  depth  and 
with  the  lowering  of  the  water  level,  as  erosion  brings  the  upper 
portion  of  the  vein  within  the  zone  of  weathering.  The  down- 
ward transportation  of  metals  or  minerals  already  in  lodes  or 
pockets  is  the  most  potent  factor  determining  the  upper  por- 
tion of  the  ore  deposit,  whose  peculiar  features  are  due  to  the 
nature  of  descending  currents.  It  is  not  infrequent  that  as- 
cending and  descending  waters  work  simultaneously.  The 
result  of  this  combined  effort  will  give  the  richest  deposits.  In 
such  cases  a  uniform  law  may  be  stated;  first,  an  increase  in 
value  with  depth  of  the  zone  of  greatest  enrichment;  second,  a 


6  ECONOMIC  GEOLOGY 

maximum  in  value  where  the  combined  efforts  of  ascending 
and  descending  solutions  are  the  greatest;  third,  a  decrease 
in  value  with  the  greater  depths. 

In  the  preceding  discussion  the  enrichment  of  ore  bodies  has 
been  effected  mainly  through  waters  of  meteoric  origin.  It 
must  not  be  forgotten  that  solutions  which  percolate  through 
fissures  and  enrich  ore  bodies  are  often  of  magmatic  origin, 
that  is,  they  are  derived  directly  from  masses  of  igneous 
material. 

In  many  cases  these  solutions  have  materially  changed  the 


FIG.  2. — Section    across  a  vein  in  the  Hillside   mine,  Yavapai  County, 
Arizona,  showing  the  ore  scattered  through  clay.     (After  Richard.} 

nature  and  value  of  mineral  deposits  previously  existing  within 
the  fissure. 

Mineral  Springs. — Mineral  springs  as  effecting  ore  deposits 
may  be  divided  into  three  distinct  classes. 

(1)  Carbonated  Waters. — Water  charged  with  carbon  dioxide 
becomes  a  potent  solvent  for  rock  constituents.  As  the  pressure 
is  lessened  this  supersaturated  solution  is  relieved  of  a  part  of 
its  burden.  The  numerous  varieties  of  travertine,  as  calcareous 
tufa  and  Mexican  onyx,  are  illustrations  of  this  type  of  material. 
Luray  Caverns  in  Virginia,  Mammoth  Cave  in  Kentucky,  and 
Limestone  Cave  in  Austria  illustrate  the  solvent  power  of 
carbonated  waters. 


ORE  DEPOSITS  7 

(2)  Solfataras. — This  includes  all  waters  in  which  sulphur  is 
present  either  as  a  sulphide,  as  hydrogen  sulphide  or  sulphur  diox- 
ide, and  sulphurous  acid.     Hydrogen  sulphide  plays  an  important 
part  in  ascending  solutions.     Its  source  is  in  the  decomposition  of 
pyrite  or  gypsum.     Its  presence  is  the  direct  cause  of  a  great 
number  of  minerals.     The  sulphide  of  the  metals  as  a  rule  is  the 
most  important  contributor  to  the  source  of  the  metal  for  com- 
merce.    Gold,  iron  and  tin  are  the  most  noteworthy  exceptions 
and  others  will  be  considered  in  the  discussion  of  the  respective 
metals. 

(3)  Thermal  Waters. — These  include  hot  springs  and  geysers. 
The  temperature  may  arise  from  meteoric  waters  percolating 
through  hot  volcanic  areas  or  magmatic  waters  slowly  working 
their  way   toward   the   surface.     More   than   one-half   of   the 
known  elements  have  been  found  in  solution  in  mineral  waters. 
The  elements  were  dissolved  in  the  mineral  waters  themselves. 
They  are  found  deposited  in  iron  and  manganese  formations 
around  mineral  springs.     They  are  dissolved  and  precipitated 
by  the  action  of  the  mineral  waters  upon  foreign  bodies. 

Origin   of   Cavities. — The   form   that   ore   bodies   assume   is 
such  as  to  prove  that  they  were  often  deposited  in  cavities  and 


FIG.  3. — Ideal  section  through  a  limestone  region  showing  caves  left  by  the 
removal  of  the  rock. 

fissures  in  the  rocks.     These  cavities  were  formed  by  numerous 
causes. 

(1)  By  acidulated  waters  dissolving  the  soluble  constituents 
of  rock  masses  as  shown  in  Fig.  3,  and  by  the  mechanical  action 
of  water,  that  is,  waters  wearing  away  material  by  the  force  of 
impact  thereby  enlarging  fissures  already  formed. 

(2)  Cavities   are   produced   by   dolomitization.     Magnesium 
carbonate  is  readily  taken  into  solution  by  carbonated  waters 
under  pressure.     If  in  the  downward  transference  of  meteoric 


8  ECONOMIC  GEOLOGY 

waters  charged  with  magnesium  carbonate  in  solution  a  stratum 
of  calcium  carbonate  should  be  encountered,  a  part  of  the  cal- 
cium would  be  exchanged  for  the  less  soluble  magnesium.  In 
time  there  would  occur  a  shrinkage  of  the  rock  mass  amounting 
approximately  to  12  per  cent.  Such  a  shrinkage  would  necessi- 
tate the  shattering  of  the  rock  mass  and  the  formation  of  cavities 
that  might  be  subsequently  filled  with  mineral  matter. 

(3)  Cavities  are  caused  by  fracturing.  Fracturing  may  be 
produced  by  a  shrinkage  as  the  direct  result  of  the  cooling. 
These  fractures  may  be  brought  into  the  zone  of  vision  through 
the  erosion  of  large  masses  of  superincumbent  strata.  If  rocks 
are  igneous  in  origin,  these  rocks  must  cool.  If  they  cool, 
they  must  shrink.  If  they  shrink,  they  must  fracture. ' 


FIG.  4. — Section  of  a  fault  formed  during  a  Japanese  earthquake.     (After 

Koto.) 

(4)  Cavities  are  produced  in  rock  masses   by  earthquakes. 
These  may  arise  through  the  intrusion  of  igneous  dikes  or  by 
volcanic  eruptions.     (See  Fig.  4.) 

(5)  Cavities  may  form  in  the   sheared   zone  of  intrusives. 
Massive  diorites  pass  into  diabases  and  then  into  hornblende 
schists  or  amphibolites.     These  amphibolites  may  metamorphose 
into  serpentine.     In  the  shearing  and  the  serpentinization  the 
crushed  areas  become  favorable  places  for  the  formation  of  ore 
bodies. 

(6)  Cavities  may  be  formed  by  the  faulting  of  the  strata 
without  the  formation  of  mountains.     This  may  arise  through 
lateral  pressure.     The  displacement,  however  small  it  may  be, 
affords  a  channel  for  the  transference  of  solutions  and  the  deposi- 


ORE  DEPOSITS 


9 


tion  of  minerals  whenever  the  conditions  become  most  favorable. 

(7)  Cavities  are  formed  in  rock  masses  by  the  principles  of 
isostacy  and  diastrophism  in  the  maintenance  of  equal  stress  as 
evidenced  in  mountain  making.  Through  diastrophism  the 
strata  become  converted  into  a  series  of  anticlines  and  synclines. 
Each  type  of  folds  often  gives  rise  to  fissures  and  a  general 
shattering  of  the  rock  mass.  While  these  two  types  of  folds 
occasion  the  greatest  disturbance,  a  pronounced  effect  is  pro- 
duced by  the  monocline  in  which  there  are  two  lines  of  yielding, 
one  at  the  crest  and  the  other  at  the  base.  These  conditions 
produce  a  favorable  environment  for  ore  bodies. 

Faults. — A  fault  is  a  fracture  or  disturbance  of  the  strata 


FIG.  5. — Ideal  section  showing  a  fracture  filled  along  a  fault  plane. 

breaking  the  continuity  of  the  formations.  (See  Fig.  5.)  As 
faults  are  usually  inclined  somewhat  to  the  horizon  there  is 
both  a  vertical  and  a  horizontal  displacement  of  the  strata, 
as  shown  in  Fig.  6.  The  throw  is  the  amount  of  the  upward 
or  the  downward  displacement  of  the  strata.  The  dip  is  the 
inclination  of  the  fault  plane  to  the  horizon.  The  hade  is  the 
inclination  of  the  fault  plane  to  the  vertical.  The  strike  is  the 
direction  of  the  outcrop  of  the  fault  plane  at  a  horizontal 
surface.  A  fault  produced  by  gravity  is  called  a  normal  fault, 
and  one  produced  by  compression  a  thrust  fault,  yet  it  is  possible 
in  a  few  instances  that  normal  faults  have  been  produced  by 
compression.  It  is  of  the  utmost  importance  in  mining  to  know 


10 


ECONOMIC  GEOLOGY 


LIMESTONE      IVfcJ   QUARTZ. 

COAfWC  SANDSTONE 

FINE    .TAN  DJ  TONS  fmof  CU  AY 


FIG.  6. — Section  showing  both  vertical  and  horizontal  faulting  of  a  vein, 
Enterprise  mine,  Rico,  Colorado.     (After  Richard.} 


FIG.  7. — Illustrations  of  single  veins  repeated  by  faulting  that  left  the 
different  pieces  parallel. 


ORE  DEPOSITS 


11 


the  system  of  faulting  that  prevails  in  a  given  district,  in  order 
that  the  ore  body  may  be  encountered  again  with  the  least 
possible  expenditure  of  both  time  and  money.  (See  Fig.  7.) 


FIG.  8. — Section  across  the  reefs  of  the  Rand  showing  the  faulting.     (After 
Hatch  and  Chalmers.) 

Schmidt's  law  is  usually  followed  which  is  as  follows:  "If  the 
fault  dips  or  hades  away  from  the  workings,  the  continuation 
is  down  the  hade.  If  it  dips  toward  the  workings,  it  should 
be  followed  upward"  (Fig.  8). 


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FIG.  9. — Quartz  vein  along  the  foot  wall  of  a  porphyry  dike,  with  stringers 
running  off  into  the  porphyry.     (After  Lindgren.) 

Veins. — The  United  States  Supreme  Court  has  denned  a  vein 
as  any  belt  or  zone  of  mineral  rock  lying  within  the  boundaries 


12  ECONOMIC  GEOLOGY 

clearly   defined   as   separating  it   from   the   surrounding  rock. 
Mineral  veins  fall  into  three  distinct  classes: 

(1)  Fissure   Veins  or   True   Veins  of  Fracture. — A  fissure  is 
of  indefinite  length  traversing  strata  independent  of  bedding, 
generally  nearly  vertical  and  filled  with  mineral  matter.     The 
fissure  is  not  parallel  to  the  bedding.     The  walls  may  or  may 
not  coincide,   and  are  nearly  parallel  with   each  other.     The 
fissure  was  in  the  rock  prior  to  the  filling.     The  fissure  vein 
then  is  the  filled  fissure,  which  is  of  indefinite  length.     It  is 
from  the  fissure  veins  that  our  largest  supply  of  the  precious 
metals  comes.     (See  Fig.  9.) 

(2)  Gash  Veins. — Gash  veins  are  represented  by  a  metalli- 


FIG.  10. — Gash   vein   in   the   magnesian  limestone  of  Wisconsin.     (After 

Chamberlain.) 

ferous  deposit  found  only  in  limestones  and  confined  to  a  single 
layer  or  formation.  They  are  the  most  common  in  the  bedding 
and  the  joint  planes.  (See  Fig.  10.) 

(3)  Segregated  Veins. — These  correspond  to  the  planes  of 
bedding  or  stratification  and  in  many  respects  are  not  unlike 
true  fissure  veins  or  gash  veins.  These  veins  vary  in  thickness 
and  direction.  Their  irregularities  are  many.  They  are  often 
pinched  out  as  by  forcing  the  walls  together,  or  by  the  ex- 
pansion due  to  tension  of  the  rock  masses,  or  solution  of  the 
walls  of  the  original  channel.  These  veins  also  vary  much  in 
richness.  The  hanging  wall  is  that  part  of  the  country  rock 
lying  geologically  immediately  above  a  vein  or  bed.  The  foot 


ORE  DEPOSITS  13 

wall  is  the  lower  boundary  of  a  lode.  The  selvage  is  the  zone  of 
clay  or  decomposed  rock,  or  both,  separating  the  vein  material 
from  its  walls  (Fig.  11). 

The  Occurence  of  Metalliferous  Veins.— (1)  Metalliferous 
veins  occur  mostly  in  disturbed  and  highly  metamorphosed 
regions.  The  tilting  and  the  folding  causes  fissures  that  may  be 
subsequently  filled  with  mineral  matter.  Mineral  veins  therefore 
occur  most  frequently  in  mountainous  regions  or  in  the  regions 
dis  turbed  by  igneous  activities.  The  lead  deposits  of  Missouri 
are  an  exception  to  the  rule  for  these  occur  in  undisturbed  and 
fossiliferous  Paleozoic  limestones. 


FIG.  11. — A  vein  with  its  ores  extending  into  the  altered  country  rock. 

(2)  These  veins  are  more  abundant  in  the  older  geological 
formations.     There  is  no  relation  between  the  occurrence  of  min- 
eral veins  and  age  alone.     The  connection  is  with  metamorphism, 
which   is   more  common  in  the  older  terranes.     In  the  Pacific 
coast  belt  metalliferous  veins  often  occur  in  Jurassic,  Cretaceous 
and  Tertiary  formations.     But  these  terranes   have  been  sub- 
jected to  folding  and  metamorphism. 

(3)  Parallel  veins  usually  have  the  same  metallic  content. 
(Veins  at  right  angles  may  in  some  cases  be  exceptions.)     The 
parallel  fissures  were  formed  by  the  same  causes,  at  the  same  time 
and  filled  with  similar  material.     Fissure  veins  not  parallel  with 


14 


ECONOMIC  GEOLOGY 


each  other  (save  perhaps  at  right  angles)  were  formed  at  different 
times  and  filled  under  different  conditions.  The  east  and  west 
veins  at  Cornwall,  England,  carry  tin  and  copper  and  are  pre- 
Triassic.  The  northeast  and  southeast  veins  are  post-Triassic, 
but  also  contain  tin  and  copper.  The  north  and  south  veins  are 
Cretaceous  and  contain  lead  and  iron. 

The  Richness  of  Veins. — (1)  If  two  mineral  veins  intersect 
each  other  one  or  both  are  generally  richer  at  the  point  of  inter- 
section. This  increased  value  may  be  due  to  the  reaction  of 
waters  bearing  different  bases  in  solution  in  the  two  fissures. 


FIG.  12. — Section  showing  the  form  of  the  ore  body  in  the,  Victor, 
Smuggler  Lee  and  Buena  Vista  miners,  Cripple  Creek  district,  Colorado. 
A,  Ore.  (After  Penrose.) 

(2)  Mineral  veins  are  likely  to  be  richer  near  their  intersection 
with  either  acid  or  basic  intrusives.     This  is  especially  true  in 
regions  that  have  suffered  much  metamorphism.     It  shows  the 
influence  of  heat  upon  the  metallic  contents  of  the  veins. 

(3)  A  change  in  the  character  of  the  county  rock  which  a  vein 
traverses  may  determine  a  change  either  in  the  contents  or  in  the 
richness  of  the  vein  material.     A  vein  may  be  well  defined  in  the 
sedimentaries  in  close  proximity  to  an  acid  or  basic  intrusive  but 
upon  invasion  of  the  igneous  rocks  the  vein  is  often  subdivided 
into  numerous  branches. 

Irregularities  in  Veins. — (1)  Fissure  veins  are  often  irregular, 
as  shown  in  Fig.  12.  The  vein  often  divides  into  numerous 


ORE  DEPOSITS 


15 


White  Porphyry 
Blue  Limestone 

|':r-y-:V.':-^;|  Gray  Porphyry 


Vein  Material 
White  Limestone 


FIG.  13.— Section  on  the  gold  ore  chute  of  Iron  Hill,  Leadville,  Colorado. 

(After  Blow.) 


FIG.  14. — A  troop  of  horses  with  the  vein  passing  around  it  on  both  sides. 
A,  Country  rock;  H,  horse;  F,  fault. 


16 


ECONOMIC  GEOLOGY 


branches.     This  is  especially  true  as  a  vein  passes  from  the  sedi 
mentaries  into  the  associated  intrusives  (Fig.  13). 


FIG.  15. — Ore  bearing  quartz  vein,  somewhat  lens-shaped.     The  country 
rock  is  altered,  but  contains  no  ore.     (After  Lindgren.) 

(2)  Veins  often  dividing  may  come  together  as  one  vein  and 
enclose  a  portion  of  the  country  rock.  Such  an  enclosed  portion 
is  called  a  "  horse. "  Several  masses  of  rock  may  appear  within 


FIG.  16. — A  vein  brecciated  on  one  side  and  banded  on  the  other. 

the  vein  and  then  they  are  called  a  "troop  of  horses,"  as  shown 
in  Fig.  14. 


ORE  DEPOSITS 


17 


(3)  Veins  may  pinch  together  by  the  creeping  of  the  strata  of 
the  wall.     In  such  cases  the  walls  are  mashed  and  the  veins 
filled  in  part  at  least  by  the  pressure  of  the  superincumbent  weight. 

(4)  Veins  may  widen  out  and  rise  to  lens-shaped  ore  masses 
within  the  vein  (Fig.  15). 

(5)  They  may  also    be  made  irregular   by  repeated  crustal 
movements,  which  break   the  rock   into   rubble-like  material. 
The  filling  of  these  incipient  fracture  planes  gives  rise  to  the  brec- 
ciated  veins,  as  shown  in  Fig.  16. 

(6)  Irregularities  are  also  formed  by  the  solution  of  limestones 
by  percolating  waters,  charged  with  carbon  dioxide. 


Granite. 

Altered  Schor/aceous 
Granite. 

Peach  with  Cassiterite. 
'ombs  of  Quartz. 

Siliceous  Iron  Ore 

Combs  of  Quartz 

Peach  with  Cassiterite. 

Altered  Schor/aceous 
Granite. 

Granite 


FIG.  17. — Structure  of  a  lode  at  the  Bellau  mine,  St.  Just,  Cornwall,  Eng- 
land.    (After  Thomas  and  MacAlister's  Geology  of  Ore  Deposits.) 

Ribbon  Structure. — A  banded  or  ribbon  structure  is  not  uncom- 
mon in  the  veins.  In  fact,  according  to  LeConte,  it  is  as  common 
in  veins  as  the  columnar  structures  is  in  dikes.  The  layers  upon 
the  two  sides  usually  correspond  with  each  other  in  color  or  in 
composition,  and,  therefore,  gives  rise  to  a  beautiful  striped  ap- 
pearance. Sometimes  these  successive  layers  are  of  different 
2 


18  ECONOMIC  GEOLOGY 

materials.  Occasionally  where  the  gangue  is  quartz  the  layers  are 
of  agate,  save  the  center,  which  presents  a  comb-like  structure  of 
interlocking  quartz  crystals,  as  shown  in  Fig.  17.  Sometimes 
there  appears  to  have  been  successive  openings  and  fillings  of  the 
fissure  both  with  the  gangues  and  the  metallic  minerals.  This  is 
considered  by  many  geologists  as  conclusive  proof  of  the  filling 
of  fissures  from  solutions. 

Age  of  Veins. — The  age  of  veins  is  determined  by  the  manner 
of  their  intersection.  The  intersecting  vein  is  always  younger 
than  the  intersected.  The  geological  period  to  which  fissure 
veins  belong  must  be  determined  by  the  fossil  content  of  the  as- 
sociated terranes  and  by  the  stratigraphical  position  or  the  litho- 
logical  similarity  of  the  contiguous  areas  in  which  the  fissures  were 
formed.  The  filling  of  the  fissure  with  gangue  and  metallic  min- 
erals is  a  slow,  subsequent  operation. 

Classification  of  Ore  Deposits. — The  classification  of  ore  de- 
posits is  a  matter  of  convenience.  It  generally  depends  upon  the 
purpose  desired.  They  may  be  classified  as  to  their  mode  of 
occurrence,  as  fissure,  lens-shaped,  bedded,  etc.  The  following 
classification  is  based  mainly  upon  use.  Metals,  precious  and 
useful. 

PRECIOUS. — Gold,  silver,  platinum,  etc. 

USEFUL. — Copper,  iron,  aluminum,  zinc,  and  lead.  Fuels: 
coal,  petroleum,  gas,  naphtha,  paraffine.  Lubricants:  graphite 
and  oil.  Structural:  granite,  limestone,  sandstone,  clay.  Orna- 
mental: phosphates,  onyx,  marble,  amber.  Fertilizers:  limestone, 
marl,  feldspars,  phosphate.  Explosives:  diatomaceous  earth. 
Miscellaneous:  asbestos,  paint. 

They  may  be  classified  as  to  origin  for  the  origin  of  economic 
products  is  as  widly  different  as  the  products  themselves.  Prof. 
J.  F.  Kemp  gives  the  following  terse  order:  Solution,  igneous, 
suspension.  Prof.  Franz  Prosepny  gives  them  Idiogenous,  that 
is  contemporaneous,  xenogenous,  that  is  later  than  the  rock. 
Prof.  W.  0.  Crosby  gives  them  Igneous,  aqueo-igneous,  aqueous. 

The  following  classification  has  been  arranged  by  W.  H.  Weed. 

A.  Igneous  magmatic  segregation, 
(a)    Siliceous. 

1.  Masses.    Aplite  masses.    Ehrenberg,  Shartash. 

2.  Dikes.    Beresite  or  aplite.    Berezovsk. 

3 .  Quartz  veins .   Alaska,  Randsburg,  B lack  Hills,  S .  D 


ORE  DEPOSITS  19 

(b)  Basic. 

1.  Peripheral   masses.     Copper,   iron,   nickel.     Sud- 
bury,  Ontario. 

2.  Dikes.  Titaniferous  iron.     Adirondacks  and  Wy- 
oming. 

B.  3.  Igneous    emanations.     Deposits     formed    from    gases 

above  or  near  the  critical  point,  e  g.,  365°  C.  and  200 
atmospheres  for  H20. 

(a)  Contact-metamorphic  deposits. 

1.  Deposits  confined  to  contact.     Magnetite  deposits 
(Hanover,   New  Mexico);   chalcopyrite   deposits, 
Kristiana  type;  gold  ores,  Bannock,  Idaho,  type. 

2.  Deposits    impregnating    and    replacing    beds    of 
contact  zone.     Chalcopyrite  deposits,  pyrrhotite 
ores,  magnetite  ores,  Canada  type;  gold  tellurium 
ores,  Elkhorn  type;  arsenopyrite  ores,  Similkameen 
type. 

(b)  Veins  closely  allied  to  magmatic  and  to  Division  D. 

1.  Cassiterite.     Cornwall,  Eng. 

2.  Tourmaline  copper.    Sonora,  Mex. 

3.  Tourmaline     gold.      Helena,     Montana;     Minas 
Geraes,  etc. 

4.  Augite  copper,  etc.  Tuscany. 

C.  Fumarolic  deposits. 

(a)  Metallic  oxides,  etc.,  in  clefts  in  lava.     No  commercial 
importance.     Copper,  iron,  etc. 

D.  Gas-aqueous  or  pneumato-hydato-genetlc  deposits,  igne- 
ous emanations,  or  primitive  water  mingled  with  ground  water. 

(a)  Filling  deposits. 

1.  Fissure  veins. 

2.  Impregnation  of  porous  rock. 

3.  Cementation  deposits  of  breccia. 

(b)  Replacement  deposits. 

1.  Propylitic.     Comstock,  Nevada. 

2.  Sericitic,  Kaolinic,   calcitic,   copper-silver,   silver- 
lead.     Clausthal,  De  Lamar,  Idaho. 

3.  Silicic  dolomitic,  silver-lead.     Aspen,  Colorado. 

4.  Silicic  calcitic.     Cinnabar,  California. 

5.  Sideritic    silver-lead.     Coeur    d'    Alene,     Idaho; 
Slocan,    B.C.;    Wood    River,    Idaho. 

6.  Biotitic  gold-copper.     Rossland,  B.  C. 


20  ECONOMIC  GEOLOGY 

7.  Fluoric  gold  tellurium.     Cripple  Creek,  Colorado. 

8.  Zeolitic.     Michigan  copper  ores. 

STRUCTURE,  TYPES  OF  THE  CLASSIFICATION  UNDER  D 

Fissure  veins:  San  Juan,  Colorado.  Volcanic  stocks:  Nagyag 
and  Cripple  Creek.  Contact  chimneys:  Judith.  Dike  replace- 
ments and  impregnations.  Bedding  or  contact  planes:  Mercur, 
Utah.  Axes  of  folds:  Synclinal  basins,  anticlinal  saddles. 
Bendigo,  Elkhorn. 

E.  Meteoric  waters.     (Surface  derived.) 
(a)  Underground. 

1.  Veins.  Wisconsin  lead  and  zinc. 

2.  Replacements.     Iron  ores,  Michigan.    Lead,  zinc, 
Mississippi  Valley. 

3.  Residual.     Gossan  iron  ores,  manganese  deposits. 
Virginia. 

(b)  Surficial. 

1.  Chemical.  Bog  iron  ores,  sinters      Some  bedded 
iron  ores,  etc.    Clinton  ore,  New  York. 

2.  Mechanical.     Gold   and  tin  placers.     California, 
Alaska. 

F.  Metamorphic    deposits.     Ores    concentrated    from    older 
rocks  by  metamorphism,  dynamo  or  regional. 

What  Constitutes  a  Mine? — (1)  In  the  broadest  sense  a  mine 
may  be  said  to  consist  of  a  body  of  ore  sufficiently  large  and 
rich  to  pay  for  the  original  purchase  price  of  the  property,  all 
costs  of  mining,  transportation,  reduction  plant,  together  with 
a  large  percentage  of  interest  on  the  investment. 

(2)  In  determining  what  constitutes  a  mine,  it  is  necessary 
to  consider  each  item  of  possible  expense  chargeable  against 
the  property,  all  physical  and  geological  conditions,  and  such 
ore  bodies  as  are  developed,  together  with  their  bearing  upon 
future  ore  bodies. 

(3)  The    situation    of    property    is    exceedingly    important. 
In  this  connection  it  becomes  necessary  to  consider  availability 
of  water,  for  power,  for  the  treatment  of  the  ore,  and  for  the 
removal  of  slimes;  fuel  as  a  source  of  heat,  and  as  a  source  of 
power;  and  timber  for  the  shafts  and  underground  workings. 
It  is  necessary  to  consider  the  accessibility  of  property  both 


ORE  DEPOSITS  21 

for  the  purpose  of  shipping  supplies  to  the  mines  and  marketing 
the  ore  or  bullion;  the  question  of  dumping  ground  for  the  re- 
moval of  waste;  the  position  of  the  mill  for  the  reduction  of  the 
ore,  and  position  of  the  smelter  for  roasting  the  ore. 

(4)  The  geological  and  physical  problems  in  connection  with 
determining   the   mine   deal  perhaps  more  with  the  future  of 
the  mine  than  with  the  actual  cash  value.     In  this  connection 
one  must  consider  not  only  the  enclosing  rocks,  their  resistance, 
definition    and   influence   upon   the   mineralization,    but   must 
consider  also  the  fissure  deposits,  if  they  are  present,  the  faults, 
because  in  the  majority  of  deposits  the  ore  actually  occurs  in 
fissures  and  faults,  or  as  fissure  veins. 

(5)  Fissures  and  faults  are  additionally  important  because  in 
many  cases  the  continuity  of  the  ore  body  must  be  determined. 
If  faulted  by  intersecting  fissures,  this  must  be  known  and  the  con- 
sequence actually  determined.     It  is  a  well-known  fact  that  ore 
bodies  are  more  often  irregular  in  dip,  strike,  and  formation  than 
otherwise,  the  valuable  portion  of  ore  being  controlled  by  some 
physical  fact  such  as  the  intersection  of  the  fissure  with  certain 
strata  whose  definition  is  known,  intersection  of  fissure  with  the 
igneous  rocks,  and  intersection  of  one  fissure  with  another  of  dif- 
ferent age.     In  a  known  district  it  is  often  possible  by  careful 
observation  of  these  facts  to  calculate  the  exact  position  of  valu- 
able bodies.     At  Rico,  Colorado,  vertical  veins  intersect  a  zone 
of  disturbance  rich  at  the  point  of  intersection.     This  has  been 
proven  generally  true.     Therefore,  wherever  vertical  veins  in- 
tersect a  plane  of  disturbance,  rich  ore  deposits  are  more  likely 
to  be  encountered. 

(6)  Ore  above  or  below  water  level  is  important  on  account  of 
the  method  of  treatment  of  the  ore.     Above  water  level  there  are 
frequently    high-grade  ores  that  can  be  quickly  and    cheaply 
reduced  by  a  simple  mill  upon  the  ground,  whereas  below  water 
level  the  milling  process  may  be  involved  and  expensive  as  it  may 
be  necessary  to  smelt  the  ores  before  reduction  to  the  metallic  state. 
These  are  very  important  items  in  the  cost  of  reduction  because 
of  the  additional  expense  required  and  the  uncertain  factor  or 
the  cost  of  reduction. 

(7)  It  is  also  necessary  to  say  whether  the  ores  are  primary 
or  secondary  in  origin.     Often  there  is  a  zone  in  the  vein  wherein 
are  deposited,  below  water  level,  very  rich  bodies  of  ore  which 
under  normal  conditions  might  reasonably  be  considered  perma- 


22  ECONOMIC  GEOLOGY 

nent.  Experience  has  shown  that  the  deep  ores  even  at  a  greatly 
increased  expense  of  mining  may  be  mined  at  a  profit.  Butte 
shows  a  zone  of  oxidation,  a  zone  of  sulphide  enrichment,  and  a 
zone  of  permanent  value  in  which  the  workings  may  be  carried 
far  below  the  surface  and  still  obtain  a  definite  value  of  metal. 
The  Michigan  copper  mines  and  the  gold  mines  on  the  west  coast 
of  British  Columbia  are  examples  of  mines  far  below  the  surface 
carried  on  at  a  profit  in  the  zone  of  permanent  value,  as  the  owners 
know  exactly  what  to  depend  upon. 

(8)  The  gross  value  of  ore  deposits  is  to  be  determined  only 
by  actual  measurement^  ores  blocked  out  and  the  determination 
of  the  values  by  careful  and  conscientious  sampling  with  sufficient 
precaution  to  assure  the  owner  that  the  results  are  absolutely 
correct.  It  is  a  very  easy  matter  to  guess  on  the  quantity  of  ore, 
but  it  would  be  an  easy  matter  to  make  an  overestimate  or  under- 
estimate, for  the  only  estimate  that  can  receive  credence  is  that 
based  upon  the  ores  actually  blocked  out.  It  is  an  easy  matter 
in  the  sampling  of  ore  chutes  to  arrive  at  an  erroneous  conclusion 
by  a  failure  to  sample  the  material  of  an  entire  vein  and  find  where 
the  value  lies.  If  the  purpose  is  to  find  out  the  value  of  an  entire 
vein,  samples  are  collected  in  different  places;  one  from  near  the 
center,  one  near  the  hanging  wall,  one  near  the  foot  wall,  one  from 
across  the  top  of  the  adit,  one  from  the  center,  and  one  from  near 
the  bottom  of  the  vein  exposed.  This  method  will  not  only  tell 
where  the  pay  streak  lies,  but  also  give  the  average  of  the  entire 
face. 

Ore  bodies  like  other  bodies  have  three  dimensions  and  there- 
fore can  be  blocked  out  only  by  actual  development.  These  ore 
bodies  must  be  cut  and  drifted  upon  at  sufficient  intervals  to 
determine  length,  thickness,  and  form  of  the  valuable  chutes. 
The  ore  bodies  may  be  divided  into  three  classes: 

(1)  Ore  actually  in  sight;  (2)  ore  technically  in  sight;  and  (3) 
ore  that  under  the  conditions  existing  should  be  expected  with 
proper  development  of  the  property. 

(10)  The  next  step  is  the  determination  of  the  method  of  min- 
ing and  treatment  of  the  ores  for  all  time  and  whatever  grade  and 
kind,  and  to  calculate  the  cost  of  converting  ore  into  money. 
Here  are  11  factors:  Cost  of  mining,  labor  and  supplies;  cost  of 
development,  labor  and  supplies;  cost  of  reduction;  teaming; 
milling;  loss  in  mill;  loss  in  smelting;  commission  paid  to  smelter; 
cost  of  equipment  of  mine;  cost  of  equipment  of  mill;  cost  of 


ORE  DEPOSITS  23 

equipment  of  smelter;  cost  of  mill;  cost  of  smelter;  cost  of 
managing  smelter;  cost  of  normal  litigation  that  may  arise  from 
ore  bodies  coming  from  other  than  the  ground  in  question; 
amount  of  interest  on  the  money  advanced  for  the  original 
purchase  and  equipment  at  nominal  rates;  and,  lastly,  a  large 
percentage  of  profit.  To  be  a  profitable  mine  the  sum  total  of 
these  costs  must  not  exceed  the  gross  value  of  the  ore  as 
calculated. 


CHAPTER  II 
ORIGIN  OF  ORE  DEPOSITS 

Meteoric  Origin. — In  the  light  of  the  new  planetesimal  hypothe- 
sis of  the  earth's  origin  which  has  been  so  admirably  worked  out 
by  Prof.  T.  C.  Chamberlain  there  seems  to  be  a  continuous  shower 
of  extraterrestial  material  falling  upon  the  surface  of  the  earth. 
If  this  material  strikes  the  land  it  mingles  with  the  soil  almost 
unnoticed.  If  it  falls  into  the  sea  its  high  specific  gravity 
carries  the  material  to  the  ocean  bottom  where  it  is  buried  in 
the  muds  ot  the  sea  floor.  If  it  falls  upon  the  Arctic  snow 
fields  it  enters  into  the  ice  and  imparts  the  peculiar  banded 
appearance  characteristic  of  so  many  glaciers.  Wherever  this 
shower  of  meteoric  dust  may  fall  it  becomes  a  possible  source  of 
ore  deposits  through  segregation  by  vadose  waters. 

Number  of  Meteorites. — According  to  Prof.  C.  A.  Young 
from  15,000,000  to  20,000,000  of  meteorites  enter  the  earth's 
atmosphere  every  24  hours.  One  of  the  most  noted  of  modern 
meteoric  masses  is  that  of  the  Canyon  Diablo  which  fell  in 
eastern  Arizona.  C.  R.  Keyes  says  that  20  miles  east  of  the 
San  Francisco  mountains,  in  the  midst  of  the  vast  level  plain 
forming  the  general  surface  of  the  high  plateau,  is  a  low  mound 
called  Coon  Butte.  The  center  of  this  butte  contains  a  crater- 
like  depression  about  1000  ft.  across.  In  the  vicinity  of  this 
hill  such  large  amounts  of  meteoric  iron  have  been  found  from 
time  to  time  as  to  give  rise  to  the  theory  that  the  crater  was 
produced  by  an  enormous  meteorite  striking  the  earth  at  this 
point.  The  impact  caused  the  fragments  to  scatter  in  all 
directions.  Meteorites  are  scattered  over  widespread  areas 
rather  than  of  local  occurrence.  The  reports  of  the  Challenger 
expedition  cite  a  great  abundance  of  chondrones  of  cosmic  origin 
in  the  abyssmal  deposits  of  the  ocean.  Nordenskjold  cites  the 
presence  of  minute,  black,  metallic  particles  in  the  Arctic  snow 
fields.  C.  R.  Keyes  calls  attention  to  hailstones  containing 
fine  metallic  particles  composed  mainly  of  iron,  nickel,  cobalt 
and  copper.  He  also  cites  the  constant  occurrence  of  meteorites 

24 


ORIGIN  OF  ORE  DEPOSITS  25 

in  the  desert  regions  of  the  Mexican  plateau  situated  many  miles 
from  the  mountains  and  far  away  from  igneous  rocks. 

Metallic  Content  of  Meteorites. — Nearly  all  of  the  common 
metals  have  been  found  in  meteorites  and  gold  has  been  reported. 
As  these  particles  reach  the  earth  they  mingle  with  the  soil, 
oxidize  in  the  presence  of  moisture,  pass  into  solution  and  are 
transported  to  a  deeper  zone  by  the  circulating  ground  waters. 
It  is  probable  that  a  part  at  least  of  the  widely  diffused  metallic 
content  of  sedimentary  rocks  is  of  meteoric  origin,  and  that 
this  extraterrestrial  material  is  the  primary  source  of  many  vadose 
ore  deposits. 

Segregation. — Many  ore  bodies  are  so  intimately  associated 
with  masses  of  igneous  rocks  as  to  lead  the  observer  to  the 


XwC>\*7 

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r  JT  JT  *•  V  >r  -V  W   * £*   -V •*«•     ^  C  3  Sr .  *^i * 


AW*  •*•**'  v.  w  **w*  'vg  ;^.v>£X 

FIG.  18. — Example  of  a  contact  deposit  between  two  different  kinds  of  rock. 

conclusion  that  such  deposits  resulted  without  doubt  from  the 
solidification  of  homogeneous  or  heterogeneous  magmas  through 
various  causes  of  differentiation.  Such  deposits  are  so  closely 
related  petrographically  to  the  rock  masses  as  to  lead  to  the 
conclusion  that  they  form  one  heterogeneous  complex.  Magmas 
may  be  either  homogeneous  or  heterogeneous.  If  the  magma 
be  homogeneous  under  the  same  conditions  of  temperature  and 
pressure,  there  is  uniform  mobility  in  the  various  portions  of 
the  material.  If  the  magma  be  heterogeneous  then  the  more 
fluid  portions  may  move  readily  toward  the  surface  and  the 
heavier  and  more  basic  material  migrate  toward  the  lower 
portion  of  such  a  magma.  These  magmas  in  which  a  perfect 
segregation  may  occur  are  deep-seated  deposits  brought  into 
view  through  the  erosion  of  a  considerable  amount  of  super- 


26 


ECONOMIC  GEOLOGY 


incumbent  strata.  (See  Fig.  18.)  In  the  process  of  segregation 
of  the  ecomonic  minerals  three  classes  of  ore  deposits  are  formed : 
(1)  The  metals;  (2)  the  oxides  of  the  metals;  and  (3)  the 
sulphides  of  the  metals.  Following  the  separation  of  the  metallic 
content,  the  oxides  and  the  sulphides  of  the  metals,  there  appears 
the  solidification  of  the  ferro-magnesian  minerals  as  the  pyroxenes, 
the  amphiboles,  etc.  After  the  solidification  of  the  ferro- 
magnesian  minerals  comes  a  more  acidic  product  as  the  feldspars 
and  the  last  to  separate  is  quartz.  (See  Fig.  19.)  The  causes  of 
segregation  are:  (1)  Fractional  crystallization  of  the  various 


•^        Mica  Syenite 
§  Porphyry 

^Igneous  Vein  showing 
5^  marginal  segregation 


FIG.  19. — Vein  of  mica  syenite-porphyry,  showing  marginal  segregation  oi 
ferro-magnesian  minerals  and  iron  ores.     (After  J.  H.  L.  Vogt.) 

constituents  of  the  magma.  (2)  The  separation  of  the  magma 
into  two  immiscible  solutions,  that  is,  solutions  that  will  not 
mix,  like  water  and  oil.  The  completeness  of  the  segregation 
may  be  determined  by  the  rate  of  cooling  of  the  magma  as  a 
whole.  (3)  The  degree  of  viscosity.  The  viscosity  will  depend 
largely  upon  the  chemical  composition  of  the  masses,  varying 
with  the  relative  amount  of  the  ferro-magnesian  and  acidic 
minerals  present.  A  segregation  of  the  magma  is  not  impossible 
before  its  appearance  as  an  intrusive  and  this  gives  rise  to  ore 
bodies  not  unlike  those  segregating  from  homogeneous  magmas, 
but  the  segregation  is  less  complete. 


ORIGIN  OF  ORE  DEPOSITS 


27 


We  may  consider  one  type  in  the  segregation  of  ore  bodies 
from  an  ultra-basic  magma  traversing  the  Appalachian  belt 
from  Alabama  to  Nova  Scotia,  appearing  often  in  the  Carolinas, 
Maryland,  -Pennsylvania,  Vermont  and  Quebec  in  a  belt  of 
Paleozoic  rocks  pierced  here  and  there  by  peridotite.  The 
segregation  in  the  Thetford  and  Black  Lake  districts,  Quebec, 
is  as  follows,  as  shown  in  Fig.  20. 

(1)  The  metals,  chromium  and  iron,  become  oxidized  and 
form  lens-shaped  masses  of  chromite  and  magnetite.  There 
is  a  tendency  for  the  chromite  and  magnetite  to  migrate  toward 
the  periphery  of  the  mass  and  to  appear  often  as  lens-shaped 
ore  bodies  in  the  midst  or  in  the  border  of  the  basic  peridotite. 
The  peridotite,  rich  in  ferro  magnesian  minerals  was  the  second 


FIG.  20. — Section  to  illustrate  the  segregation  of  chromite  and  magnetite  as 
lens-shaped  ore  bodies,  Troy,  Vermont.     A,  Perdotite;  B,  sericite  schist. 

mass  to   solidify.     The  peridotite   consists  almost  entirely  of 
the  ferro  magnesian  mineral  olivine. 

If  a  difference  existed  in  the  constituents  of  the  magma  the 
pyroxenites  would  appear  third  in  the  process  of  solidification. 
The  next  product  in  the  order  of  the  solidification  was  acidic  in 
character,  light  in  color,  of  lower  specific  gravity,  and  the  product 
a  granite  containing  crystals  of  the  potash  feldspar,  orthoclase, 
with  granules  of  some  ferro  magnesian  minerals,  usually  horn- 
blende. The  final  product  as  a  rock  mass  from  solidification  is 
the  most  acidic  and  ribbed  by  veins  of  aplite,  in  which  the  feld- 
spars, micas  and  amphiboles  are  apparently  absent.  The  final 
product  through  the  differentiation  of  the  ultra-basic  magma 
gives  free  silica  or  quartz. 


28  ECONOMIC  GEOLOGY 

No  scientist  has  ever  worked  more  indefatigably  in  the  prod- 
ucts of  magmatic  segregation  than  J.  H.  L.  Vogt.  His 
classification  gave  us:  (1)  The  segregation  of  the  native  metals; 
(2)  the  segregation  of  metallic  oxides;  and  (3)  the  segregation 
of  metallic  sulphides.  In  the  segregation  of  the  metals,  the  pre- 
cious metals,  gold,  silver,  and  platinum  are  formed. 

(1)  Silver,  the  least  frequently  occurring  as  an  original  mineral, 
is  in  such  form  and  quantity  as  to  lead  to  the  conclusion  that  the 
metal  followed  the  law  of  solidification  of  magmas  from  the 
basic  to  the  acidic.     Gold  is  found  in  considerable  quantities  in 
the  basic  rocks  as  diabases  and  diorites,  and  in  such  acidic  rocks 
as  the  granites  and  syenites;  examples  of  the  latter  are  found  in 
the  pegmatites  of  Australia  and  Alaska.     The  platinum  is  a 
product  of  segregation  from  such  ultra-basic  rock  masses  as  the 
peridotites  and  the  modern  form  or  appearance  is  as  grains  of 
platinum  associated  with  the  metamorphic  products.     In  serpen- 
tine platinum  is  almost  always  associated  with  the  segregation 
of  chromite,  although  all  chromite  does  not  contain  platinum. 
The  most  important  segregation  of  metallic  iron  is  manifested 
at  Disco  Island,  on  the  western  coast  of  Greenland  where  large 
masses   having   the    appearance   of   meteoric    iron   have   been 
discovered.     It  was  not  until  the  ore  body  was  subsequently 
discovered  in  place  that  its  true  nature  was  known,  viz.,  segrega- 
tion from  the  basic  intrusive  basalt. 

Cobalt  and  nickel  are  more  or  less  common  and  wherever  one 
is  found  the  other  is  present.  Perhaps  in  New  Zealand  is  found 
the  best  illustration  of  ore  bodies  of  cobalt  and  nickel  segregating 
from  a  molten  magma.  This  generally  carries  a  certain  per- 
centage of  iron,  so  it  becomes  an  alloy  of  cobalt  and  iron. 

(2)  The    second   class  of  products   segregating  from  molten 
magma  is  the  metallic  oxides.     Types  of  chromite  and  magnetite 
are  among  the  more  important  and  more  common.     In  many 
cases   the   titanium   is   so    abundant   in  magnetite  as  to  lead 
to  the  conclusion  that  the  titanium  oxide  plays  the  role  of  an 
acid,  and  the  iron  that  of  the  base.     Illustrations  are  common 
in  the  formation  of  such  ore  bodies  in  the  Adirondack  Mountains 
in  New  York. 

Another  mineral  sometimes  segregating  as  an  original  mineral 
is  cassiterite.  In  general,  however,  it  is  associated  with 
pegmatite,  an  acid  product  in  the  solidification  of  some  magma. 
In  certain  sections  the  character  of  the  ore  body  is  such  as  to 


ORIGIN  OF  ORE  DEPOSITS 


29 


lead  one  to  the  conclusion  that  it  is  an  original  mineral.  In 
the  peridotite  belt  that  stretches  from  Alabama  to  Nova  Scotia, 
in  North  Carolina  especially,  corundum  occurs  in  considerable 
abundance  as  an  original  mineral  and  emery  is  found  in  Massa- 
chusetts. The  former  has  the  formula  A1203  and  the  latter 
contains  hematite  or  magnetite  intimately  mixed  with  corun- 
dum. These  original  minerals,  surpassed  in  hardness  only  by  the 
diamond,  are  worthy  of  mention  here  for  their  use  as  abrasives. 
(3)  The  third  class  as  worked  out  by  Vogt  was  that  of  the 
metallic  sulphides.  The  segregation  of  metallic  sulphides  is 
characteristic  of  several  types  of  igneous  rocks  as  a  result  of  dif- 
ferentiation either  before  or  after  intrusion.  They  are  common 


FIG.  21. — Section  to  illustrate  the  mode  of  occurrence  of  sulphidic  segre- 
gations connected  with  norite  intrusions.  1,  Norite;  2,  pyrite;  3,  gneiss. 
(After  Thomas  and  MacAlister's  Geology  of  Ore  Deposits.} 

products  of  segregation  from  magmas  rich  in  ferro  magnesian 
minerals.  The  sulphides  commonly  occurring  with  igneous  origin 
are  copper,  iron,  cobalt  and  nickel.  (See  Fig.  21.)  Associated 
with  these  are  the  arsenides  of  a  few  metals.  These  are  less  im- 
portant and  need  not  be  further  considered.  The  sulphide  of 
copper  most  commonly  segregating  is  chalcopyrite,  CuFeS2. 
Bornite  and  chalcocite  may  also  occur  as  primary  minerals. 

Pneumatolysis. — Pneumatolysis  demands  the  formation  of  ore 
bodies  from  both  acid  and  basic  intrusives  through  the  agency  of 
gases  dissolved  in  the  magmas.  Because  the  gases  were  present 
at  the  time  of  the  intrusion,  they  were  under  high  pressure  and 
above  their  critical  temperature.  The  magmatic  vapors  and 


30  ECONOMIC  GEOLOGY 

steam  are  liberated  during  the  consolidation  of  deep  seated  intru- 
sives.  The  action  takes  place,  not  before  consolidation  begins, 
but  during  the  process  of  consolidation  and  ceases  altogether 
when  solidification  is  complete.  The  vapors  extract  the  metals 
from  the  cooling  magma  and  deposit  them  as  oxides  and  sulphides. 
Without  pneumatolytic  action  the  metals  within  the  magma 
would  remain  as  accessory  minerals  in  the  form  of  oxides,  sul- 
phides, or  silicates,  distributed  through  the  rock.  If  these  metals 
be  present  in  sufficient  quantities  to  become  essential,  they  pro- 
duce a  massive  segregation. 

Pneumatolysis,  therefore,  is  the  process  of  extracting  metals 
from  deep  seated  magma  by  the  agency  of  superheated  gases. 
The  ores  are  deposited  in  the  fissures  and  joint  planes,  both  in 
the  igneous  rocks  and  the  adjacent  metamorphic  aureole.  The 
character  of  the  minerals  in  the  lodes  is  determined  by  the  type 
of  magma  from  which  they  were  derived.  The  classification  of 
such  ore  deposits  depends  upon:  (1)  The  nature  of  the  rock  giv- 
ing rise  to  the  ores.  (2)  The  particular  metals  contained  in  the 
cooling  magma.  (3)  The  minerals  associated  with  the  ore  bodies! 

The  gases  are  called  carriers  or  mineralizers.  Each  magma  has 
its  own  mineralizer,  and  whether  the  metals  will  be  deposited  as 
oxides  or  sulphides  depends  upon  their  chemical  affinity  and  the 
presence  or  absence  of  sulphur.  Tin,  as  will  be  shown  later,  is 
most  abundant  as  the  oxide  even  when  sulphur  is  present  in  the 
magma,  while  lead  is  most  abundant  as  the  sulphide. 

By  the  active  magmatic  gases  the  metalliferous  minerals  spar- 
ingly scattered  through  the  cooling  mass  are  withdrawn  and  more 
or  less  concentrated  in  the  partially  consolidated  intrusive.  The 
gases  are  then  liberated  and  the  ores  concentrated  in  the  lodes 
in  which  they  are  found,  either  in  the  intrusive  or  in  the  walls. 

The  third  step  is  the  liberation  of  thermal  waters.  The  tran- 
sition from  concentration  of  minerals  to  liberation  of  thermal 
waters  is  gradual.  The  character  of  the  ore  bodies  is  deter- 
mined by  the  nature  of  the  fissures,  joints,  faults,  breccias,  bed- 
ding planes,  or  other  cavities  in  which  deposition  has  taken 
place.  The  form  of  the  deposit  is  of  the  utmost  importance 
to  the  miner.  To  the  geologist  the  altered  walls  of  the  lode 
and  the  minerals  of  the  lode  determine  the  character  of  the 
magma  from  which  the  ore  was  derived.  According  to  Thomas 
and  MacAlister,  the  most  typical  pneumatolytic  ores  are  cas- 
siterite,  wolframite,  and  scheelite,  which  may  be  associated  with 


ORIGIN  OF  ORE  DEPOSITS 


31 


sulphide  of  copper,  iron,  and  arsenic,  and  less  commonly  ores 
of  the  other  metals.     (See  Fig.  22.) 

Cassiterile. — Lodes  of  tin  are  characterized  by  the  presence  of 
minerals  bearing  fluorine.  This  active  element  is  able  at  high 
temperature  to  form  a  volatile  compound  with  tin,  which  at  a 
lower  temperature  is  deposited  as  cassiterite  according  to  the 
equation : 

SnF4+2H2O  =  Sn02+4HF. 

Fluorine  bearing  minerals  in  the  country  rock  owe  their  exist- 
ence to  the  presence  of  free  hydrofluoric  acid.  Boron,  chlorine, 


FIG.  22. — Tin  lode  at  the  Bunny  Mine,  St.  Austell,  Cornwall,  England. 

(After  Thomas  and  MacAlister's  Geology  of  Oie  Deposits.) 
"The  vein  infilling  is  coarse  cavernous  quartz,  with  a  distant  resemblance 
to  comby  structure.     It  is  a  pegmatite  vein  containing  cassiterite  and  wol- 
framite, some  feldspar  in  the  vein  is  kaolinized  and  the  adjacent  granite  is 
altered  to  greisen,  A  little  fluorite  and  tourmaline  are  present." 

carbon  dioxide,  and  occasionally  sulphur  aie  piesent.  These 
vapors  also  assist  in  the  extraction  of  the  metals  from  the  magma. 
Fluorine  also  forms  a  volatile  compound  with  silicon  and  the 
silica  associated  with  tin  veins  may  have  been  formed  accord- 
ing to  the  equation: 


32  ECONOMIC  GEOLOGY 

When  the  intruded  rock  is  traversed  by  numerous  joint  planes, 
the  vapors  decompose  its  various  constituents  and  readily  form 
new  minerals.  If  the  country  rock  is  not  traversed  by  joints  the 
process  begins  along  planes  of  bedding  or  cleavage  planes  of  min- 
erals and  the  alteration  is  easily  effected.  Feldspars  are  kao- 
nized  and  micas  chloritized.  Silicification  of  the  country  rock 
and  greisenization  also  are  not  uncommon,  but  the  character  of 
the  change  depends  upon  the  nature  of  the  magmatic  vapors. 

Fluorine  belongs  to  the  earliest  emanations  but  boron,  carbon 
dioxide,  and  hydrogen  sulphide  may  belong  either  to  the  early 
or  later  emanations. 

Order  of  Deposition. — At  Cornwall  both  the  oxide  of  tin  and  the 
sulphide  ores  were  simultaneously  deposited.  The  presence 
of  copper  ores  upon  previously  formed  cassiterite  leads  to  the 
conclusion  that  copper  ores  continued  to  be  deposited  after  the 
deposition  of  tin  had  ceased.  In  other  instances  where  tin  and 
copper  ores  arrived  simultaneously,  cassiterite  was  deposited 
first. 

Thomas  and  MacAlister  give  the  order  of  deposition:  (1)  Cas- 
siterite and  wolframite,  together  with  the  sulphides  of  copper, 
iron  and  arsenic.  (2)  The  sulphides  of  copper,  iron  and  arsenic, 
associated  with  those  of  lead,  silver  and  cobalt.  (3)  Silver  sul- 
phides and  the  oxides  and  carbonate  of  iron.  (4)  Nickel,  anti- 
mony, and  manganese  minerals. 

The  intrusion  came  in  as  large  batholites  of  granite  cutting 
sedimentaries  of  Ordovician  Age.  At  Central  and  East  Corn- 
wall they  cut  through  Devonian  rocks.  The  smaller  batho- 
lites at  Devonshire  cut  Devonian  and  Carboniferous  strata. 
The  ore  is  concentrated  either  in  the  periphery  of  the  granite 
batholith  or  the  metamorphic  aureole. 

The  copper  ores,  containing  chalcopyrite,  chalcocite  and 
bornite,  where  tin  does  not  occur,  are  often  of  pneumatolytic 
origin.  In  Norway  where  copper  lodes  are  associated  with  a 
greisenized  granite,  the  ore  is  unquestionably  formed  under 
the  principles  of  pneumatolysis. 

At  Copperfield,  Strafford  and  Corinth,  Vermont,  the  chal- 
copyrite, associated  with  tourmaline,  occurs  in  saddle-shaped 
bodies  in  mica  schist,  or  in  chimneys  at  the  contact  of  granite 
veins  with  mica  schist.  Pyrite  and  pyrrhotite  are  the  associated 
sulphides.  These  sulphides  were  formed  under  pneumatolytic 
conditions. 


ORIGIN  OF  ORE  DEPOSITS  33 

Gold.  —  Gold  is  sometimes  found  in  copper-tourmaline  veins 
connected  with  intrusives.  It  is  found  principally  in  the  quartz 
and  the  tourmaline  lies  near  the  walls  of  the  vein.  This  is 
especially  true  in  Thelemarken.  In  Ontario  auriferous-tourma- 
line veins  occur  in  which  the  walls  of  the  country  rock  are 
well  tourmalinized. 

Titanite,  rutile,  anastase,  and  brookite  are  minerals  often 
formed  by  pneumatolytic  action  associated  with  fluorine  and 
boron-bearing  minerals.  Molybdenite  is  also  found  in  quartz 
veins,  pegmatites  and  granites  in  such  manner  as  to  show  pneu- 
matolytic action. 

The  Basic  Intrusives.  —  Ore  bodies  associated  with  the  basic 
intrusives,  gabbros  and  diabases,  are  often  markedly  pneumat- 
olytic, but  not  as  common  as  in  the  granites,  yet  the  process 
is  the  same.  The  principal  agent  or  mineralizer  is  chlorine 
instead  of  fluorine  or  boron.  Titanium  would  be  extracted  as 
the  chloride  and  deposited  as  the  oxide  according  to  the  equation  : 

TiCl4+2H20  =  Ti02+4HCl. 
Iron  is  similarly  extracted: 

Fe2Cl6+3H20  =  Fe203+6HCl. 
The  reactions  of  phosphorus  and  lead  are  similar: 


PbCl2+H2S  =  PbS+2HCl. 

Fluorine  and  boron  are  rare  in  the  basic,  but  common  in  the 
acid  intrusives. 

Hydatogenesis.  —  Hydatogenesis  is  the  process  by  which  ore 
bodies  connected  with  the  intrusives  of  basic  and  acidic  magmas 
are  formed  outside  the  metamorphic  aureole.  In  point  of  time 
they  are  generally  post-pneumatolytic.  If  it  happens  to  be 
contemporaneous  then  it  must  take  place  beyond  the  zone  of 
metamorphism.  If  they  appear  in  the  aureole  or  in  the  igneous 
rock  itself,  they  were  not  formed  until  solidification  and  meta- 
morphism were  complete.  When  the  zone  of  metamorphism  is 
free  from  minerals  indicating  mineralizers,  the  lode  may  be 
considered  to  belong  to  the  hydatogenetic  class.  The  ores  are 
sulphides  and  oxides  of  the  metals,  the  former  predominating. 
To  determine  whether  the  ore  body  is  of  pneumatolytic  or 
hydatogenetic  origin,  the  geologist  must  look  first  to  the  nature 


34 


ECONOMIC  GEOLOGY 


of  the  irruptive  rock  from  which  the  minerals  were  derived; 
second,  to  the  nature  of  the  minerals  in  the  lode,  and  third,  to 
the  character  of  the  non-metalliferous  minerals  both  in  the 
lode  and  the  metamorphic  aureole.  The  magma  may  have 
been  either  basic  or  acid,  deep-seated  or  superficial,  irruptive 
or  eruptive. 

In  the  classification  of  hydatogenetic  deposits,  it  is  customary 
to  select  the  most  important  economic  mineral.  Many  deposits 
are  catalogued  as  gold  ores  that  are  strictly  pyritic  lodes  charac- 
terized by  a  small  amount  of  gold. 

Primary  Gold  Veins. — Hydatogenetic  gold  veins  are  associated 


FIG.  23. — Section  to  illustrate  the  formation  of  auriferous  quartz  lenses  in 
alaskite.     (After  Thomas  and  MacAlister's  Geology  of  Ore  Deposits.) 

with  granite,  porphyry,  andesite,  trachyte  and  rhyolite.  (See 
Fig.  23.)  The  chief  gangue  is  quartz,  but  calcite,  siderite  and 
magnesite  may  be  present  with  the  quartz.  Barite  and  fluorite 
may  form  the  gangue;  tourmaline  and  orthoclase  may  also  be 
present.  In  what  form  the  gold  was  extracted  from  the  rocks 
and  transported  is  perhaps  uncertain.  The  solutions  were  di- 
lute and  the  gold  reduced  to  the  elemental  state  by  the  accom- 
panying sulphides.  The  presence  of  carbon  or  hydrocarbons 
in  the  walls  of  the  ore  body  aids  in  its  enrichment.  In  the 
secondary  concentration  near  the  surface  melanterite  has  been 
the  precipitant.  Gold  may  occur  as  a.  telluride  of  gold,  or 


ORIGIN  OF  ORE  DEPOSITS  35 

telluride  of  gold  and  silver,  or  free  gold  in  the  presence  of  other 
tellurides.  It  occurs  with  the  auriferous  silver  ores  and  with 
the  sulphides  of  other  metals  in  which  the  gold  is  present  in  the 
elemental  state  not  as  a  sulphide. 

Primary  Copper  Ores. — Chalcopyrite,  chalcocite  and  bornite 
appear  as  primary  minerals  of  hydatogenetic  origin.  The 
native  copper  is  either  metamorphic  or  metasomatic  in  origin. 
The  chalcopyrite  is  by  far  the  most  important  contributor  to 
the  world's  supply  of  copper,  but  not  all  chalcopyrite  is  primary. 
The  sulphides  are  derived  from  either  acid  or  basic  intrusives 
and  precipitated  by  the  action  H2S  in  the  heated  waters. 

Primary  Lead  and  Zinc  Ores. — The  sulphides  of  lead  and  zinc, 
when  filling  fissures,  appear  to  be  connected  with  acid  intrusives 
and  are  most  abundant  in  the  Paleozoic  rock  although  they 
appear  in  the  rocks  of  all  ages.  It  is  from  these  intrusives  that 
the  lead  and  zinc  minerals  appear  to  have  been  derived. 

Primary  Silver  Ores. — True  silver  veins  are  characterized  by 
the  presence  of  original  argentiferous  minerals  as  native  silver 
and  argentiferous  alloys  together  with  the  chlorides,  iodides, 
bromides,  selenides,  tellurides,  antimonides,  arsenides  of  silver 
and  other  metals. 

In  Butte,  Montana,  the  silver  seems  to  have  been  derived 
from  dikes  of  quartz  porphyry  cutting  granites.  At  Cobalt, 
South  Lorraine  and  Gowganda,  Ontario,  the  silver  is  derived  from 
diabase  and  gabbro;  therefore  primary  silver  deposits  may  be 
associated  with  either  acid  or  basic  intrusives. 

The  sulphides  of  the  other  metals  also  appear  as  primary  ores, 
when  derived  from  some  magma  and  precipitated  by  hydrogen 
sulphide.  Two  carbonates  appear  as  hydatogenetic  minerals, 
siderite  and  rhodochrosite;  one  hydrosilicate  garnierite  is  derived 
from  a  peridotite  magma  in  its  transition  to  serpentine  and  de- 
posited in  the  numerous  fissures  by  the  combined  action  of 
lateral  secretion  and  hydatogenesis. 

Metasomasis. — According  to  Le  Conte,  metasomasis  is  the 
process  by  which  change  in  the  mineral  composition  of  a  rock  is 
effected.  It  may  be  produced  in  three  ways:  (1)  By  the  alter- 
ation of  the  original  minerals;  (2)  by  the  replacement  of  the 
original  minerals;  (3)  by  the  crystallization  of  the  minerals. 
The  three  changes  may  be  effected  separately  or  conjointly. 

If  a  limestone  should  be  replaced  in  part  by  magnesium  carbon- 
ate and  therefore  converted  into  dolomite,  such  a  dolomitization 


36 


ECONOMIC  GEOLOGY 


would  represent  a  metasomatic  replacement.  The  replacing 
material  is  introduced  by  circulating  meteoric  waters.  The  sol- 
vent action  of  the  water  is  increased  by  the  presence  of  carbon 


FIG.  24. — Contact  deposits  in  limestone  beneath  shale. 

dioxide  under  pressure,  sulphides  and  silicates,  together  with  the 
humic  acid  of  the  soil. 

Where  sedimentaries  lie  in  contact  with  igneous  rocks,  iron 
is  leached  out  of  the  intrusive  and  by  chemical  action  deposited 


FIG,  25. — Iron    ores    of  Michigan  interbedded  with  sedimentary    rocks. 

(After  Emmons.) 

as  an  iron  ore  wherever  an  equivalent  amount  of  limestone  has 
been  dissolved  and  transported  elsewhere  by  percolating  waters 
(Fig.  24).  Metasomatic  metalliferous  minerals  are  most  com- 
mon in  the  sedimentary  rocks.  They  may  be  deposited  soon 


ORIGIN  OF  ORE  DEPOSITS 


37 


after  the  deposition  of  the  sediments  on  the  floor  of  the  sea,  or 
some  later  period,  either  before  or  after  these  sedimentaries  have 
become  land  masses. 

Ore  deposits  thus  formed  are  divided  into  two  classes:   (1) 
Bedded  deposits,  in  which  the  ore  body  conforms  with  the  strata 


FIG.  26. — Iron  ores  of  Michigan  interbedded^with  igneous  and  sedimentary 
rocks.     (After  Emmons.} 

in  which  it  lies,  as  shown  in  Figs.  25,  26,  and  27.  (2)  Fissure 
deposits,  in  which  the  ore  conforms  to  the  fissures  and  joints  of 
the  strata  which  may  cross  the  sedimentaries  at  any  angle. 
The  former  type  embraces  the  most  important  iron  and  man- 


FIG.  27. — Geological  section  in  the  manganese  region  of  north  Arkansas. 
The  block  bands  represent  beds  of  manganese  that  were  deposited  in  layers 
alternating  with  the  accompanying  rocks. 

ganese  formations,  while  the  latter  includes  the  silver,  lead  and 
zinc  deposits. 

There  are  three  ways  of  recognizing  a  metasomatic  ore  body: 

(1)  The  absence  of  symmetrical  banding  of  its  vein  material. 

(2)  The  absence  of  breccias  cemented  by  gangue  minerals.     (3) 
Lack  of  definition  between  the  country  rock  and  the  ore  body. 


38 


ECONOMIC  GEOLOGY 


Metasomatic  Iron  Ores. — The  ores  of  iron  that  owe  their  origin 
to  chemical  action  through  solution  and  precipitation  are  the 
carbonate  (siderite),  the  oxide  (hematite)  and  the  hydrous  oxide 
(limonite).  (See  Fig.  28.) 

The  source  of  the  iron  is  generally  some  neighboring  intrusive 
or  pyritiferous  sedimentary.  The  iron  is  dissolved  by  percolating 
waters.  The  solutions  may  find  their  way  into  strata  capable  of 
effecting  the  chemical  change  suggested,  or  find  their  way  into 


FIG.  28. — Section  to  illustrate  the  usual  occurrence  of  iron  ore  deposits 
in  the  Mesabi  range.  It  is  below  the  glacial  drift  and  resting  upon  quartz- 
ite.  (After  Winchell) 


standing  waters  where  the  iron  can  be  extracted  and  deposited 
by  metasomatic  action. 

Pyrite  will  oxidize  readily  to  melanterite,  FeSO4,7H2O.  Solu- 
tions bearing  calcium  carbonate  will  bring  about  the  reaction 
through  which  the  iron  would  be  precipitated  as  the  carbonate 
and  the  calcium  sulphate  will  be  precipitated  as  gypsum,  CaSO4,- 
2H2O,  or  transported  elsewhere. 

FeSO4 + CaCO3  =  FeCO3  +  CaS04. 

If  the  percolating  waters  bear  chlorine,  the  chloride  of  iron, 
Fe2Cl6,  will  be  formed  and  calcium  carbonate  acting  upon  the 


ORIGIN  OF  ORE  DEPOSITS 


39 


chloride  of  iron  will  precipitate  the  iron  as  the  oxide  (hematite), 
according  to  the  equation: 


The  iron  ore  replaces  the  lime- 
stone in  the  metasomatic  de- 
posits molecule  by  molecule. 

Thomas  and  Mac  A  lister 
divide  the  iron  ores  of  metaso- 
matic origin  into  two  classes: 
(1)  Contemporaneous,  in 
which  the  replacement  oc- 
curred either  during  or  im- 
mediately after  the  deposition 
of  the  original  rock.  (2)  Sub- 
sequent, in  which  the  replace- 
ment occurred  after  the  depo- 
sition and  consolidation  of  the 
original  rock.  The  former  in- 
cludes the  bedded  deposits 
and  the  latter  the  irregular 
patches  and  veins.  The  oolitic 
Clinton  iron  ore  of  central 
New  York,  Pennsylvania  and 
Alabama  is  a  representative 
of  the  contemporaneous  de- 
posits. The  ore  lies  above  the 
Medina  sandstone  in  lime- 
stones of  Silurian  age. 

The  Lake  Superior  iron  ores 
lie  upon  the  Archean  complex 
and  in  the  Keweenawan  ter- 
ranes.  They  form  the  best 
American  representative  of 
subsequent  replacement.  (See 
Fig.  29.) 

The  source  of  the  iron  seems 

to  have  been  the  ancient  igneous  rock  of  the  Lake  Superior 
region.  The  iron  was  precipitated  as  siderite.  The  siderite 
then  passed  into  hematite  and  insensibly  into  ferruginous 
quartz  schists,  jaspers,  magnetite  and  limonite  schists.  In  the 


40 


ECONOMIC  GEOLOGY 


Mesabi  district  the  iron  was  originally  deposited  as  the  silicate, 
greenalite. 

Metasomatic  deposits  of  Bauxite. — The  Georgia- Alabama  baux- 
ites are  found  in  -Paleozoic  limestones  above  pyritiferous  shales. 
Meteoric  waters  oxidize  the  pyrite  to  ferrous  sulphate  and  sul- 
phuric acid.  The  free  acid  attacks  the  aluminum  silicates  of  the 
shales  producing  alum  and  aluminum  sulphates  which  are  carried 
upward  by  ascending  currents.  These  solutions,  in  contact  with 
the  overlying  limestones,  form  calcium  sulphate  and  bauxite. 

Lead  and  Zinc  Metasomatic  Deposits. 
— Lead  and  zinc  form  metasomatic 
ores  in  the  form  of  the  sulphides,  sul- 
phates, carbonates  and  silicates.  The 
sulphides  are  of  most  importance. 
Such  deposits  are  common  in  the  Car- 
boniferous limestone  but  may  occur 
in  the  limestones  of  any  age.  In 
Cumberland,  England,  the  ore  takes 
the  form  of  and  replaces  the  calca- 
reous fossils.  The  molecular  replace- 
ment has  been  so  perfect  that  the  ore 
preserves  not  only  the  external  form 
but  often  the  internal  structure  of  the 
fossils  it  has  replaced. 

The  source  of  the  lead  and  zinc  min- 
erals is  often  in  some  igneous  rocks  or 
sulphide-bearing  sediments.  These 
may  be  beneath  the  surface  or  exposed  to  weathering  agencies  at 
the  surface.  The  transporting  waters  are  meteoric  and  carry  the 
solutions  downward  where  deposition  takes  place  (Fig.  30). 

Metasomatic  Copper  Deposits. — Chalcopyrite,  CuFeS2,  is  the 
most  important  copper  ore  of  metasomatic  origin.  The  materials 
came  from  some  igneous  magma  during  the  later  stage  of  its 
cooling.  The  aqueous  emanation  transported  the  minerals  in 
the  form  of  sulphates.  The  solutions  are  either  ascending  or 
descending  and  the  chalcopyrite  would  be  precipitated  by  hydro- 
gen sulphide  and  alkaline  sulphides.  If  the  solution  percolated 
through  the  limestone,  then  malachite  and  azurite  would  be 
formed. 

Metasomatic  Gold  Deposits. — According  to  Thomas  and  Mac- 
Alister,  in  the  Transvaal  district,  siliceous  gold-bearing  solutions 


FIG.  30. — Diagrammatic 
section  showing  the  contact 
of  porphyry  and  limestone 
and  the  zone  of  ore  deposi- 
tion, Maginnis  mine,  Judith 
Mountains,  Montana.  (After 
Weed  and  Pirsson.) 


ORIGIN  OF  ORE  DEPOSITS  41 

acting  upon  pyrite  below  the  permanent  water  level,  in  the  pres- 
ence of  a  deficiency  of  oxygen  caused  a  partial  oxidation  of  the 
pyrite  and  a  consequent  metasomatic  deposition  of  the  gold. 

Precipitation. — Precipitation  is  the  process  by  which  certain 
constituents  of  a  solution  are  rendered  insoluble  in  that  solution. 
This  is  effected  in  the  laboratory  by  the  lowering  of  the  tempera- 
ture, by  the  evaporation  of  the  solvent,  or  by  double  decomposi- 
tion. In  nature  the  fall  of  temperature  occurs  with  rising  ther- 
mal waters,  but  ores  thus  precipitated  would  be  rare.  The 
evaporation  of  the  solvent  is  common  and  metallic  ores  may  thus 
be  thrown  out  of  solution.  The  most  common  cause  of  precipi- 
tation is  the  mingling  of  different  solutions  in  the  trunk  channels. 

Siderite  and  rhodochrosite  are  held  in  solution  in  waters  charged 
with  carbon  dioxide.  If  the  carbon  dioxide  be  extracted  by 
relief  of  pressure,  or  by  any  other  cause,  these  metals  are  repre- 
cipitated  as  carbonates  and  remain  as  such  in  the  absence  of 
oxidizing  agents.  The  sulphides  of  many  metals  are  precipitated 
from  their  sulphate  solution  by  the  action  of  organic  matter,  or 
by  the  action  of  hydrogen  sulphide  upon  their  acid  solution, 
while  others  are  precipitated  as  sulphides  from  their  alkaline 
solutions.  Precipitated  bedded  ores  may  occur  as  sheets  be- 
tween sedimentaries,  or  as  crystals,  grains,  or  nodules  in  the 
sedimentaries. 

These  deposits  may  be  recognized:  (1)  By  parallelism  with 
the  enclosing  sedimentaries;  (2)  by  their  occurrence  in  different 
horizons;  (3)  their  margins  are  clearly  defined;  and  (4)  they  do 
not  shade  into  the  barren  country  rock. 

Iron  and  Manganese  as  Oxides. — These  occur  as  bog-ores. 
Iron  and  manganese  are  thrown  out  of  solution  as  a  mixture  of 
hydrated  oxides  by  the  action  of  algae  and  bacteria.  Siderite 
may  be  brought  into  solution  by  percolating  waters  and  when 
oxidized  thrown  out  of  solution  as  ferric  hydroxide,  according  to 
the  equation: 

4FeC03  +  02+3H2O  =  Fe2(OH)6+Fe203+4C02 

The  primary  source  of  the  iron  and  manganese  is  the  ferro- 
magnesian  silicates  of  the  igneous  rocks.  The  pyrite  of  the  sed- 
imentaries also  is  oxidized  or  decomposed  by  humic  acid  and 
rendered  available  for  precipitation.  These  minerals  of  iron  and 
manganese  had  their  primary  source  in  the  igneous  rocks  which 
furnished  the  detritus  from  which  the  sedimentaries  were  formed. 


42 


ECONOMIC  GEOLOGY 


In  carbonaceous  shales  the  iron  and  manganese  minerals  are 
precipitated  as  carbonates  by  the  loss  of  carbon  dioxide  from 
their  solutions  and  the  reducing  action  of  organic  matter.  The 
ore  deposits  thus  precipitated  occur  either  as  continuous  sheets 
or  as  bands  of  concretionary  minerals.  (See  Fig.  31.) 

The  sulphides  of  these  metals  occur  as  precipitates  in  bedded 
deposits  either  through  the  action  of  H2S  upon  their  solutions 
or  by  the  reduction  of  their  soluble  sulphates.  In  the  Harz 
Mountains,  the  sulphide  of  copper  occurs  in  bedded  deposits  that 
appear  to  have  been  reduced  from  sulphate  solutions  by  the  action 
of  decomposing  organic  matter. 

Gold  is  precipitated  in  siliceous  sinter  in  Queensland,  Australia, 


FIG.  31. — Limonite    concretions    in    the    Kittany  Valley,    Pennsylvania. 
(Photograph  by  T.  C.  Hopkins.} 

where  the  sinter  has  been  deposited  from  highly  alkaline  siliceous 
waters.  This  ore  has  yielded  over  $350  per  ton  in  gold. 

A  few  precipitates  as  silicates  are  well  known.  Illustrations 
may  be  cited  in  the  greenalite  of  the  Mesabi  iron  district,  Min- 
nesota, and  the  glauconite  or  green  sand  marl,  of  New  Jersey. 

Metamorphism. — Metamorphism  is  the  process  by  which  a 
complete  or  nearly  complete  chemical  change  has  been  effected 
in  an  ore  body.  These  changes  may  take  place  either  in  the  upper 
part  of  lodes  and  bedded  masses  exposed  to  percolating  meteoric 
waters  or  at  considerable  depths  below  the  surface  by  thermal 
and  dynamic  agencies.  The  first  implies  the  downward  trans- 
ference of  minerals  in  solution  for  the  subsequent  enrichment  of 
metalliferous  deposits;  the  second,  the  reconstruction  of  an  ore 


ORIGIN  OF  ORE  DEPOSITS  43 

body  or  rock  mass  by  the  influence  of  high  temperature  or  by 
shearing  stresses  of  sufficient  intensity  to  generate  considerable 
heat.  The  heat  necessary  for  metamorphism  may  arise  from  the 
intrusion  of  a  fluid  magma  or  from  the  internal  heat  of  the  earth. 
Dr.  F.  W.  Clarke,  in  his  "Data  of  Geochemistry"  cites  the  follow- 
ing changes  as  the  most  important: 

(1)  Molecular  Rearrangement. — By  this  process  a  pyroxene  is 
converted  into  an  amphibole. 

(2)  By  Hydration. — The  conversion  of  a  peridotite  or  a  pyrox- 
enite  into  a  serpentine  or  steatite  would  represent  the  change. 

(3)  By  Dehydration. — Limonite,  2Fe203,Fe2(OH)6,  is  converted 
into   hematite,  Fe203,  and  bauxite,  A1203,2H20,  into  corundum, 
A1203. 

(4)  Oxidation  and  Reduction. — Through  oxidation  ferrous  com- 
pounds become  ferric.     Through  reduction  hematite,  Fe20s,  be- 
comes magnetite,  Fe304. 

(5)  Changes  other  than  hydration  produced  by  percolating  solu- 
tions.    The  transference  of  some  cement  into  a  sandstone  and 
its  conversion  into  a  quartzite  would  be  an  example. 

(6)  Metamorphism  by  the  action  of  gases  and  vapors,  the  so-called 
"mineralizing    agents."     The  process  generates  new  minerals 
and  introduces  new  solutions. 

(7)  Metamorphism  by  Igneous  Intrusion. — By  this  process  new 
minerals  are  developed  in  the  metamorphic  aureole. 

The  ores  associated  with  metamorphic  rocks  may  be  divided: 
(1)  Into  those  which  occur  as  layers  or  lenticles  in  the  crystalline 
schists,  and  (2)  those  which  occur  as  metamorphosed  metaso- 
matic  deposits  of  irregular  shape. 

In  the  crystalline  rocks,  hematite  and  magnetite  are  often  of 
commercial  significance.  The  hematite  is  produced  by  the  dehy- 
dration of  limonite  and  the  magnetite  by  the  reduction  of  hema- 
tite or  by  the  decomposition  of  siderite  through  a  loss  of  carbon 
dioxide. 

As  sulphides,  chalcopyrite,  galenite,  sphalerite  and  pyrite  are 
common  in  Scandinavia.  While  not  of  so  great  importance  in 
themselves  alone,  they  have  been  the  source  of  the  material  for 
the  enrichment  of  the  lodes,  traversing  the  district.  The  magne- 
tite ore  bodies  of  the  Adirondacks,  New  York,  represent  a  meta- 
morphosed deposit  in  the  older  schists  and  gneisses.  (See  Figs. 
32  and  33.) 

Another  illustration  may  be  cited  in  the  famous  hematites  and 


44 


ECONOMIC  GEOLOGY 


FIG.  32. — Iron  mine,  Lyon  Mountain,  New  York.     (Photograph  by  T.  C. 

Hopkins.) 


FIG.  33. — Iron  mine,  Lyon  Mountain,  New  York.     (Photograph  by  T.  C. 

Hopkins.) 


ORIGIN  OF  ORE  DEPOSITS 


45 


magnetites  of  Constantine,  North  Africa,  noted  for  their  remark- 
able freedom  from  sulphur  and  phosphorus. 

The  zinc-manganese  mineral  franklinite  at  Franklin  Furnace, 
N.  J.,  occurs  in  a  metamorphosed  limestone  with  zincite,  wil- 
lemite  and  rhodochrosite. 

Corundum,  ruby,  sapphire  and  emery  occur  in  the  metamor- 
phosed schists  and  limestones.  The  famous  emery  deposits  on 


FIG.  34. — Map   of  the  district  of  Persberg,   showing  the  association  of 
'  the  ore  with  metamorphosed  calcareous  rocks.     (After  Sjorgren.) 

the  Island  of  Naxos  in  the  Grecian  Archipelago  occur  in  a  meta- 
morphosed limestone.  Metamorphic  ore  deposits  may  be  recog- 
nized by  their  associated  minerals  and  their  mode  of  occurrence. 
Metamorphic  contact  deposits  are  not  distributed  over  large 
areas  but  rather  confined  within  the  metamorphic  aureole  in 
which  the  change  has  been  effected  through  the  influence  of 
some  intrusive. 

The  changes  produced  in  an  ore  body  are  along  the  lines  of  de- 


46  ECONOMIC  GEOLOGY 

hydration  and  recrystallization.  The  intrusives  may  also  bring 
in  new  minerals  by  means  of  the  heated  solutions  given  off  by  the 
magma  during  the  last  stages  of  its  consolidation  which  bridges 
the  gap  between  pneumatolysis  and  metasomasis.  (See  Fig.  34.) 

Metamorphic  masses  of  hematite,  magnetite  and  pyrolusite 
occur  in  association  with  the  intruded  porphyry  at  Santiago,  in 
Cuba.  The  copper  deposits  at  Bisbee,  Arizona,  must  in  part  be 
catalogued  as  metasomatic,  yet  these  copper  ores  occur  within 
as  well  as  without  the  metamorphic  aureole  and  associated  with 
a  porphyry  magma. 

At  Deep  Creek,  Utah,  gold  occurs  as  a  metamorphic  contact 
deposit  in  masses  of  granite  and  porphyry  intruding  the  limestone. 
At  the  contact  of  the  intrusive  with  the  limestone,  garnets  and 
tremolite  occur  in  abundance.  The  gold  occurs  both  in  a  finely 
divided  state  in  the  recrystallized  limestone  and  in  threads  in 
masses  of  tremolite. 

Secondary  Changes.  —  Secondary  changes  in  ore  bodies  are 
effected;  (1)  By  oxygenated  meteoric  waters,  and  (2)  by  waters 
derived  from  depth.  The  process  often  involves  solution  and  the 
transference  downward  of  the  more  soluble  minerals  for  enrich- 
ment of  the  lodes  at  the  lower  levels.  The  extent  to  which  the 
alteration  will  extend  depends  upon:  (1)  The  relation  of  the 
rock  to  drainage;  (2)  the  level  of  the  ground  water,  and  (3)  the 
humidity  of  the  climate. 

By  glacial  erosion  in  northern  areas  and  continental  denudation 
everywhere,  the  changes  are  carried  progressively  to  lower  levels. 
In  the  secondary  changes  by  ascending  solutions  the  older  min- 
erals are  replaced  by  the  newer,  as  at  Comstock  Lode,  Nevada, 
where  calcite  is  replaced  by  quartz.  The  change  is  generally 
effected  by  solutions  of  a  later  period  of  mineralization. 

The  possibility  of  these  deep-seated  changes  was  pointed  out 
by  J.  H.  L.  Vogt,  who  showed  that  by  either  hot  air  or  super- 
heated steam,  argentite  may  be  converted  into  native  silver  and 
sulphur  dioxide  according  to  the  equations: 


Ag2S+H20  =  2Ag+H2S+0. 
or  on  copper  ores: 

2Cu2S+60  =  2Cu2O+2SO2. 

Cu2S+2Cu2O  =  6Cu-}-2SO2 

Ag3AsS3+3H2O  =  3Ag+As+3H2S+3O. 


ORIGIN  OF  ORE  DEPOSITS  47 

Weathering  changes  effected  in  the  upper  part  of  lodes  are 
in  part  oxidation  and  in  part  reduction.  The  upper  part  com- 
prises a  zone  of  oxidized  minerals.  Beneath  this  there  is  a  zone 
of  enriched  ores,  often  the  richest  portion  of  the  entire  lode,  be- 
neath which  there  is  a  zone  of  permanent  value. 

In  the  oxidation  of  chalcopyrite,  ferrous  sulphate  is  formed, 
which  is  readily  oxidized  to  ferric  sulphate.  The  ferric  sulphate 
reacts  upon  the  chalcopyrite,  reducing  the  mineral  to  chalcocite, 
and  by  further  influence  of  the  ferric  sulphate  the  chalcocite  is 
converted  into  the  sulphate  of  copper,  according  to  the  equation  : 
Cu2S+5Fe2(S04)3+4H20=2CuS04+10FeS04+4H2S04. 

The  copper  sulphate  in  solution  is  transferred  downwards  to  be 
reduced  by  the  pyrite  or  other  sulphides  according  to  the  equa- 
tions 

7CuSO4+4FeS2+4H20  =  7CuS+4FeSO4+4H2S04 
HCuS04+5CuFeS2+8H20=8Cu2S+5FeS04+8H2S04. 

The  copper  sulphate  in  the  presence  of  either  pyrite  or  troilite 
may  be  converted  into  chalcopyrite,  as,  for  example,  on  Vancouver 
Island.  The  carbonates  of  copper  are  less  soluble  than  the  sul- 
phate. If  calcium  carbonate  in  solution  is  transported  downward 
in  the  copper  lode,  malachite  or  azurite  and  calcium  sulphate 
would  be  formed  with  the  liberation  of  carbon  dioxide.  The 
chalcanthite  in  solution  may  be  reduced  to  tenorite,  2CuS04+ 
2CaC03  =  2CuO+2CaS04+2C02,  which  in  contact  with  ferrous 
sulphate  solutions  would  be  reduced  to  cuprite,  Cu20,  and  ulti- 
mately to  native  copper. 

Cerussite  and  anglesite,  the  carbonate  and  sulphate  of  lead, 
are  similarly  formed  direct  from  galenite,  while  native  silver  is 
often  produced  by  the  reducing  action  of  decomposing  pyrite 
upon  the  sulphate  of  silver. 

Detrital  Deposits. — Detrital  deposits  are  those  resulting  from 
the  disintegration  of  rock  masses  through  atmospheric  agencies. 
The  more  resistant  the  parent  rock  the  shallower  the  deposits 
become.  If  the  gradient  of  the  stream  in  the  valley  is  small,  the 
deposit  will  concentrate  near  the  source  of  the  ore.  The  higher 
the  gradient  and  the  greater  the  velocity  of  the  stream,  the  farther 
down  the  valley  the  metalliferous  minerals  will  be  carried  (see 
Fig.  35).  The  composition  of  the  detrital  deposit  will  depend 
upon  the  nature  of  the  overlying  country  rock  and  the  assorting 
power  of  the  associated  waters,  as  shown  in  Fig.  36. 


48 


ECONOMIC  GEOLOGY 


Placers  represent  the  concentration  of  the  heavier  economic 
minerals  in  the  order  of  their  decreasing  density.     In  shallow 


FIG.  35.-^-Theoretical  section  showing  the  origin  of  auriferous  gravels. 
The  dark  lines  represent  gold-bearing  veins  of  which  the  coarser  and  heavier 
materials  accumulate  in  the  valleys. 


Gabbro 


Schists  Etc. 


Limestone 
with  Iron  Ores 


FIG.  36. — Map  to  illustrate  the  influence  of  ore-bearing  rocks  on  the 
alluvia  of  streams  and  rivers.  (After  Thomas  and  MacAlister's  Geology  oj 
Ore  Deposits.) 

placers  the  metalliferous  mineral  is  confined  to  one  level.     In  the 
deep  leads  there  are  two  or  more  levels  at  which  the  values  may  be 


ORIGIN  OF  ORE  DEPOSITS 


49 


obtained.  Deep  leads  therefore  mark  a  cessation  in  the  deposi- 
tion of  sediments.  It  may  be  that  the  stream  was  turned  into 
some  other  channel  by  geological  changes  and  subsequently  re- 
turned again  to  the  same  valley.  (See  Figs.  37  and  38.) 

Laterite  is  the  name  applied  to  deposits  arising  through  the 


FIG.  37. — Section  through  Tuolumue  County,  California,  showing  old 
river  auriferous  gravels  covered  by  a  bed  of  lava,  and  the  method  of  tunneling 
to  reach  them,  at  the  sides  are  shown  river  gravels_of_a  later  age. 

solution  and  oxidation  of  certain  minerals.  The  metalliferous 
minerals  in  such  cases  lie  near  the  base  of  the  hills,  composed 
largely  of  basic  intrusives  which  have  been  the  source  of  the  ore. 
Such  deposits  are  represented  in  the  Appalachian  belt,  India, 
Madagascar  and  elsewhere. 


i 


FIG.  38. — Section  through  the  Red  Point  and  Damm  Channels  from 
El  Dorado  Canyon  (right)  to  Humbug  Canyon,  California,  showing  the 
auriferous  gravels  covered  by  lava,  and  the  method  of  reaching  them  by 
tunneling.  The  dotted  lines  at  the  sides  suggest  the  ancient  outlines  of 
the  hills. 

Gold. — Placer  deposits  are  one  of  the  most  important  sources  of 
this  precious  metal.  In  the  Black  Hills  of  S.  Dakota,  and  in 
Alaska  the  gold  has  been  concentrated  by  wave  action.  It  is 
derived  from  pre-Cambrian  metamorphics  traversed  by  quartz 
veins. 


50  ECONOMIC  GEOLOGY 

In  the  detrital  deposits  of  the  Transvaal  it  is  considered  by  some 
authorities  that  by  the  absence  of  nuggets  the  gold  must  have 
been  deposited  by  subsequent  infiltration  into  the  conglomerate 
with  which  it  is  associated.  The  arguments  in  favor  of  its  de- 
trital origin  are:  (1)  Gold  is  restricted  to  the  conglomerate;  (2) 
the  coarser  the  conglomerate  the  richer  it  is  in  gold  content; 
(3)  it  was  present  in  the  conglomerate  before  much  erosion  took 
place;  (4)  it  is  independent  of  dikes  and  faults;  and  (5)  it  is  inde- 
pendent of  those  sulphides  which  serve  as  precipitants  for  gold. 

In  Australia  the  detrital  gold  deposits  have  furnished  one  nug- 
get weighing  233  lb.,  but  as  a  mass  of  gold  weighing  140  Ib.  has 
been  found  in  quartz  reefs,  the  larger  nugget  may  be  of  detrital 
origin.  However,  through  chemical  affinity,  small  particles  of 
gold  are  often  welded  together. 

Platinum. — Platinum  is  derived  from  two  types  of  rocks,  the 
ultra-basic  and  the  basic  intrusives,  while  detrital  gold  is  often 
derived  from  both  the  acid  and  basic  igneous  rocks.  The  rare 
metals  of  the  platinum  group  as  osmium  and  iridium  are  also 
found  in  the  platinum  placers.  The  Ural  placers  are  the  richest 
in  the  world  in  platinum,  but  placers  containing  both  platinum 
and  gold  are  found  in  California. 

Iron. — Iron  occurs  abundantly  as  beach  placers  in  the  United 
States  and  New  Zealand,  but  it  is  seldom  present  in  considerable 
quantity  in  other  forms  than  oxides.  The  black  sands  of  many 
river  valleys  are  auriferous  but  they  consist  essentially  of  mag- 
netite derived  from  the  basic  intrusives  associated  with  its  genesis. 

Tin. — The  most  important  tin  deposits  of  the  world  are  de- 
trital. The  oxide  of  tin,  cassiterite  (Sn02),  stoutly  resists  dis- 
integration. During  the  erosion  of  the  granites,  pegmatites  and 
contact  metamorphics  the  tin  finds  its  way  toward  the  bottom  of 
the  detritus.  It  has  been  found  in  beach  placers  in  England  and 
in  torrential  placers  in  Bolivia. 

The  tin  deposits  of  the  Federated  Malay  States  are  the  most 
important  in  the  world.  The  acid  intrusives  forming  the  high 
lands  have  suffered  decomposition  and  erosion  and  cassiterite 
has  become  the  chief  detrital  placer  mineral. 

On  the  Islands  of  the  Banka  and  Billiton  the  tin  deposits  occur 
in  two  forms;  (1),  "shoad"  deposits  in  which  the  ore  is  found  near 
the  lodes  from  which  it  was  derived;  and  (2),  the  deep  lead  placers 
which  may  extend  over  considerable  area  and  varying  depths. 

Assorted  Minerals. — These  are  often  of  no  economic  significance 


ORIGIN  OF  ORE  DEPOSITS  51 

in  themselves  alone  but  their  constant  occurrence  in  a  placer  im- 
plies the  presence  of  a  precious  or  useful  metal.  Cinnabar  and 
wolframite  indicate  that  the  placer  may  carry  gold;  topaz  and 
tourmaline  signify  the  possible  existence  of  tin;  while  chromite  is 
an  invariable  associate  of  platinum. 


CHAPTER  III 

PRECIOUS  METALS 

GOLD,  SILVER  AND  PLATINUM 

Properties  of  Gold. — Gold,  symbol  Au,  is  a  soft  yellow  metal 
unaffected  by  either  moist  or  dry  air.  It  is  insoluble  in  all  single 
acids  save  selenic.  It  surpasses  all  other  metals  in  its  malleability 
and  ductility.  Its  specific  gravity  is  19.3;  melting-point,  1065°  C. 
and  atomic  weight,  197.2. 

Ores  Containing  Gold. — Native  gold:  Pure  Au  is  sometimes 
found  but  most  of  the  native  gold  contains  a  small  amount  of  silver 
platinum,  etc.  Petzite  (Ag,Au)2,Te:  In  ratio  of  3  :  1  the  gold 
content  would  be  25.5  per  cent.  Hessite  (Ag2Te) :  Gold  is  often 
present  replacing  a  part  of  the  silver.  Sylvanite  (Au,Ag)Te2: 
If  the  ratio  is  1:1  it  would  give  24.5  per  cent.  gold.  Calaverite 
(Au,Ag)Te2:  with  ratio  7:1  it  would  contain  39.5  per  cent, 
gold.  Krennerite  (Ag2Te,Au2Tes) :  The  per  cent,  of  gold  is  35.5. 
Nagyagite  (Au2,Pbi4,Sbs,Te7,Si7).  Some  samples  have  given  upon 
analysis  12.75  per  cent,  of  gold. 

Occurrence. — Gold  occurs  native  encased  within  quartz. 
Sometimes  in  a  finely  divided  state,  sometimes  in  particles  of 
considerable  size,  as  nuggets,  grains,  scales,  plates,  threads  and 
wires  in  quartz  rock.  It  is  often  encased  in  pyrite,  chalcopyrite, 
arsenopyrite,  magnetite  and  hematite.  It  occurs  also  in  a  finely 
divided  state  in  schistose  rocks,  often  in  too  small  quantity  to  pay 
for  profitable  extraction.  It  has  been  observed  in  the  process  of 
deposition  at  Steamboat  Springs,  Nevada.  It  is  present  in  sea 
water,  especially  along  the  coast  of  Norway.  It  has  been  detected 
in  many  saline  minerals,  as  sylvite,  kainite,  halite,  and  carnallite. 
It  has  also  been  found  in  the  ashes  of  sea  weeds.  An  attempt  was 
made  several  years  ago  to  reclaim  the  gold  from  the  sea  waters  of 
the  northeastern  coast  of  the  United  States,  and  although  the 
metal  appeared  in  considerable  quantity,  the  effort  proved  futile. 

The  percentage  of  gold  in  sea  water  varies.  It  is  present  in 
greatest  abundance  where  meteoric  waters,  flowing  freely  through 

52 


PRECIOUS  METALS  53 

gold-bearing  belts,  reach  the  sea.  In  the  Appalachian  belt,  there 
is  gold  in  the  schistose  rocks.  Therefore  along  the  Atlantic 
coast  it  is  manifestly  present  in  the  sea  water.  Australia  has 
many  gold  deposits,  and  meteoric  waters  flowing  in  rivers  to  the 
sea  naturally  carry  some  gold  to  the  sea. 

The  compounds  of  gold  occurring  as  minerals  of  economic  im- 
portance are  few.  The  combination  is  generally  with  telluruim 
as  petzite,  (Ag,Au)2Te,  in  which  the  silver  and  the  gold  vary  some- 
what but  represent  the  unit  structure  in  the  mineral. 

Hessite  shows  no  gold  in  the  formula,  Ag2Te,  but  gold  may  re- 
place the  silver  to  a  considerable  extent.  There  is  theoretically 
at  least  every  gradation  between  the  true  telluride  of  gold  on 
the  one  hand  and  the  telluride  of  silver  on  the  other.  In  the 
telluride  of  gold,  silver  is  generally  present  and  in  the  telluride  of 
silver,  gold  is  usually  found.  Calaverite,  sylvanite,  krennerite 
and  nagyagite  are  also  important  sources  of  gold.  The  last  named 
mineral  is  best  catalogued  as  a  sulpho-telluride  of  lead  and  gold. 
Kalgoorlite  and  coolgardite  are  examples  of  the  tellurides  of  gold, 
silver  and  mercury.  Gold  occurs  also  as  an  amalgam  with  mer- 
cury, and  as  an  alloy  with  copper,  bismuth,  platinum  and  rhodium. 

A  word  may  be  said  here  with  reference  to  the  occurrence  of 
gold  as  a  sulphide.  The  proofs  of  its  occurrence  as  such  are 
inadequate.  The  sulphide  of  gold  is  exceedingly  unstable  when- 
ever the  precipitation  occurs  in  chemical  laboratories  or  the  labo- 
ratory of  nature  by  the  action  of  hydrogen  sulphide  upon  the 
neutral  or  slightly  acid  solution  of  the  metal.  Its  instability 
favors  its  immediate  reduction  to  the  elemental  state,  provided 
any  reducing  agent  is  present. 

The  sulphide  of  iron  which  is  an  exceedingly  common  associate 
with  gold  serves  as  such  a  reducing  agent.  Therefore  whenever 
gold  is  found  encased  in  pyrite,  it  is  always  present  as  free  gold 
and  not  as  a  sulphide.  Therefore  the  existence  of  auric  sulphide, 
Au2S3,  in  nature  may  be  questioned. 

Gold  is  found  widely  diffused  in  nature  although  one  of  the 
scarcer  metals.  It  appears  both  in  the  igneous  rocks  and  the 
sedimentaries,  and  manifests  itself  in  the  metamorphic  rocks  both 
of  igneous  and  sedimentary  origin.  When  occurring  in  igneous 
rocks  the  ore  is  of  primary  origin;  when  in  fissure  veins  it  is  of 
pneumatolytic  origin;  when  in  sedimentary  rocks  it  is  of  secondary 
origin.  Its  favorite  gangue  mineral  is  quartz  often  associated 
with  fluorite  and  pyrite.  Its  occurrence  in  the  granites  of  Mexico 


54 


ECONOMIC  GEOLOGY 


and  their  metamorphic  derivatives  proves  that  gold  is  more  likely 
to  be  found  in  the  acidic  than  in  the  basic  rocks.  It  ha.s,  however, 
been  found  in  basic  rocks,  and  this  occurrence  is  not  rare. 


The  auriferous  quartz  veins  are  doubtless  free  from  silver  in 
most  cases.  In  some  cases,  it  has  been  suggested  by  J.  E.  Spurr 
of  the  United  States  Geological  Survey,  that  they  represent 


PRECIOUS  METALS 


55 


magmatic  segregation.  The  same  idea  has  been  advanced  by 
C.  R.  Van  Hise  of  the  University  of  Wisconsin.  Again  it  has 
been  shown  by  Thomas  and  MacAlister  in  their  "  Geology  of  Ore 


a  ^ 

'%  ^ 

o  , 

A  <tt 

co  g 


1 


W  3 


*j     O 

|3 


Deposits"  that  the  composition  of  gold  is  variable.  If  any 
metallurgical  plant  produces  gold  as  pure  as  0.999  fine  it  is  only 
by  the  most  careful  method  of  treating  the  ore. 


56 


ECONOMIC  GEOLOGY 


The  elements  associated  with  gold  are  silver,  copper,  mercury, 
platinum,  bismuth,  iron,  rhodium  and  tellurium.  Gold  occurs 
also  as  an  incrustation  upon  other  minerals,  and  deposits  on  twigs 
in  the  Hot  Springs  of  New  Zealand  have  been  found.  It  has  also 
been  detected  as  a  cement  joining  fragments  of  quartz.  These 
occurrences  all  lead  to  the  conclusion  that  secondary  gold  is  de- 
posited from  solution,  and  that  primary  gold  is  of  magmatic 
origin  (Figs.  39  and  40). 

Character  of  Ore  Bodies. — A  very  common  occurrence  of  gold 
is  in  true  fissure  veins,  even  and  perhaps  more  abundant,  in  seams 


FIG.  41. — Gold  Vein,  Cripple  Creek,  Colorado.  G,  Granite;  P,  phonolite 
A,  altered,  impregnated  granite,  with  strings  of  fluorite  and  gold  ore. 
(After  T.  A.  Richard,  U.  S.  Geological  Survey.) 

or  layers  in  close  proximity  to  the  hanging  wall,  occasionally  mi- 
grating across  the  fissure  vein  and  in  close  proximity  to  the  foot- 
wall.  Fissure  veins  often  fluctuate  in  value,  so  that  the  ore 
richest  in  gold  occurs  in  pockets,  or  " bonanzas"  as  the  miner 
says.  In  some  mining  belts  one  may  by  systematic  drifting  along 
the  direction  of  the  main  fissure  vein  encounter  a  " bonanza." 
Where  the  normal  concentration  or  value  through  the  vein  would 
be  from  $6  to  $10  per  ton,  a  pocket  might  be  represented  by  a 
richness  of  $50,000  or  even  $100,000  per  ton.  It  often  occurs  that 


PRECIOUS  METALS 


57 


drifting  along  the  line  of  the  vein  must  be  carried  for  thousands  of 
feet  in  ore  that  does  not  pay  for  the  extraction  of  the  metal  before 
such  a  pocket  is  encountered.  Again,  the  line  carrying  the  gold 
may  be  simply  a  thin  seam  or  film,  so  that  all  the  ore  workable 
with  profit  may  be  deposited  from  solution  on  a  film  so  thin  as 
to  be  almost  invisible  to  the  naked  eye.  Sometimes  the  material 
of  the  entire  vein  is  rich  enough  to  pay  for  the  profitable  extrac- 
tion of  the  metal.  This  is  especially  true  in  some  gold  mines  of 
British  Columbia  and  Alaska.  The  ores  are  more  likely  to  be 
spotted  than  otherwise,  that  is,  gold  occurs  in  small  pockets. 


FIG.  42. — Section  in  the  Elkton  mine,  Cripple  Creek  district,  Colorado, 
showing  the  relation  of  the  vein  A  to  the  dike  B  and  to  the  country  rock  C. 

(After  Penrose.) 

rather  than  with  a  uniform  distribution  throughout  the  entire 
vein.  The  vast  majority  of  gold  deposits  within  the  United 
States  occur  in  true  fissure  veins.  (See  Fig.  41.) 

The  second  type  is  known  as  the  propylitic  in  which  through 
the  metasomatic  alterations  of  the  wall  rock  there  is  developed 
secondary  minerals  such  as  chlorite  and  epidote,  the  former  re- 
sulting from  the  metamorphism  of  various  micas,  the  latter  from 
the  alterations  of  feldspars.  These  propylitic  types  are  in  close 
proximity  to  veins  of  sericite  and  kaolin.  The  first  type  occurring 
with  quartz  gangue  in  true  fissure  veins  is  seldom  highly  argenti- 
ferous, the  second  type  in  which  kaolinization  has  taken  place  is 


58  ECONOMIC  GEOLOGY 

often  rich  in  silver  content  or  highly  argentiferous.  The  char- 
acter of  the  rock  which  the  vein  traverses  is  often  variable,  for 
the  gold-bearing  veins  appear  in  either  igneous  or  sedimentary 
rocks,  sometimes  at  the  contact  zone  between  igneous  and  sedi- 
mentary rocks,  little  influenced  by  the  character  of  the  rock  which 
the  vein  traverses  save  in  the  case  of  replacement  (Fig.  42). 
Again,  true  fissure  veins,  in  the  more  recent  lava  flows,  often 
appear  intimately  associated  with  tellurium,  and  these  often  give 
rise  to  pockets  of  great  richness.  In  the  telluride  group  the  ores 
occur  either  as  definite  tellurides  of  gold  with  silver,  lead  and 
antimony,  or  as  native  gold  accompanied  with  various  tellurides. 
The  gangue  minerals  are  quartz  and  fluorite;  calcite  may  be  spar- 
ingly present.  In  Boulder  County,  Colorado,  roscoelite,  a  vana- 
dium mica,  is  associated  with  the  tellurides. 

Classification. — Gold  deposits  are  often  classified  according 
to  their  association.  The  first  of  these  may  be  catalogued  as  gravel 
deposits.  It  includes  all  classes,  whether  as  river  or  beach  gravels 
or  Covered  with  volcanic  material.  The  gold  appears  as  a  result 
of  the  disintegration  of  superincumbent  strata  where  the  gold  by 
its  insolubility  and  the  higher  specific  gravity  has  been  trans- 
ported to  lower  altitudes  in  the  adjacent  valleys.  Pay  gold  is  not 
transported  far  from  the  site  of  its  parent  rock.  The  lower  por- 
tions of  the  gravel  bed  are  generally  richer  in  gold  than  the  upper 
layers  because  of  the  higher  specific  gravity  of  the  metal.  Where 
the  rocks  are  fractured  as  by  joint  planes,  fissures,  and  the  action 
of  the  frost,  these  places  of  breakage  are  often  found  well  studded 
with  gold  so  that  2  or  3  ft.  of  the  decomposed  and  altered  bed 
rock  is  removed  for  the  extraction  of  the  gold  it  contains.  It 
seems  that  some  gold-bearing  gravels  decrease  in  richness  toward 
the  surface,  and  then  there  will  appear  a  rich  layer  of  greater  or 
smaller  width  than  the  zone  of  extreme  richness  at  the  bottom  of 
the  placer.  This  implies  that  there  was  a  cessation  in  the  de- 
livery of  auriferous  gravel,  and  then  a  return  of  the  original  stream 
to  the  valley,  carrying  a  second  contribution  of  auriferous  gravel 
over  the  same  course  as  the  former.  Ordinarily  there  is  only 
one  zone  in  the  gravel  and  that  directly  at  the  base,  but  where 
others  occur  it  must  imply  that  there  was  some  disturbance  or 
cessation  in  the  delivery. 

The  second  class  of  gold  ores  (Fig.  43)  may  be  catalogued  as 
quartzose.  This  implies  that  the  gangue  mineral  is  acid,  that  is, 
quartz,  and  that  fluorite  may  abound,  or  even  the  other  gangue 


PRECIOUS  METALS 


59 


minerals  of  the  alkaline  earth  group.  Not  infrequently  there 
appears  within  the  quartz  varying  amounts  of  pyrite,  and  even 
limited  quantities  of  copper  and  lead.  These  are  free  milling 


w~ 


F  G.  43. — Vertical  section  showing  the  forking  of  the  Pike's  Peak  vein, 
Cripple  Creek  district,  Colorado.     (After  Penrose.) 

ores.  By  a  free  milling  ore  is  meant  one  that  does  not  require 
roasting  before  amalgamation  will  take  place.  Dry  ore  is  the 
term  often  used  (Fig.  44). 


O  £   »     O    -^      £><>Oe>QO^C><>^'OOO<?O<>44<j<l   4< 

******   \«4  &******&    °*   *4<*    Q    0A«    tiJ*^ 
O    &    &          £>A*.xi^/\,.   ^^IAAX.^A-'A»OA         V«.^ 


A    ^ 


0  a  ^.^    ^  *  A  " 


4.    4.   +   +    4-4.   ^   4 


*-t+-+-f4-f-4--hf4--»- 

V.*  .+  +  *.• 


A°  A^A^AA4 

<i»^>  A.A         y,-4         •*         -O 

^^1    *    *         A*«t«**A 


FIG.  44. — Horizontal  section  in  the  Elkton  mine,  Cripple  Creek 
district,  Colorado,  showing  the  relation  of  the  vein  a  to  the  dike  b  and  to 
the  country  rock  c.  (After  Penrose.) 

The  third  class  of  gold  ores  is  auriferous  copper  ores.  These 
are  widely  distributed  throughout  the  United  States  and  much  of 
the  chalcopyrite  is  gold  bearing.  Yet  in  many  cases  the  yellow 


60  ECONOMIC  GEOLOGY 

metal  is  not  present  in  sufficient  quantity  to  warrant  its  extraction. 
These  auriferous  copper  ores  are  especially  abundant  in  Colorado, 
Utah,  Montana  and  British  Columbia.  Also  at  Gold  Hill,  North 
Carolina  and  in  Newfoundland. 

The  fourth  class  of  gold  ore  is  auriferous  lead  ores.  The  per- 
centage of  lead  is  large  and  the  gold  content  often  small.  They 
are  refactory  ores  like  the  copper  ores.  By  ref actory  ore  is  meant 
one  that  requires  roasting  before  amalgamation  will  take  place. 
The  heavy  sulphides  as  copper,  lead  and  antimony  require  this 
method  of  treatment,  that  is  the  condition  of  the  gold  in  the  min- 
eral will  not  allow  of  its  immediate  union  with  mercury  upon  the 
amalgamation  plates. 

The  fifth  class  of  gold  ores  comprises  the  gold-telluride  group. 
The  gold  telluride  ores  occur  with  silver,  or  with  silver,  lead  and 
antimony,  or  as  native  gold  accompanied  by  other,  tellurides. 
These  ores  are  often  sent  direct  to  the  smelters  for  treatment. 

Geographical  Distribution  of  Gold. — Gold  is  widely  distributed 
in  nature.  It  is  present  in  almost  all  rocks,  but  only  in  a  few 
localities  in  sufficient  quantity  for  profitable  extraction.  If  a 
line  is  drawn  from  Lake  Winnipeg  on  the  north  southwesterly  to 
the  eastern  base  of  the  Rocky  Mountains  and  from  thence 
southerly  to  the  Rio  Grande  River,  nine-tenths  of  all  the  gold  of 
the  United  States  lies  west  of  that  line. 

The  American  belt  then  may  be  divided  into  five  areas :  (1)  The 
Appalachian  region,  (2)  the  Black  Hills  region;  (3)  the  Cordilleran 
region;  (4)  the  Pacific  Coast  belt,  and  (5)  the  Alaskan  belt. 

Appalachian  Region. — The  Appalachian  field  stretches  in 
a  northeasterly  direction  from  Alabama  on  the  south,  to  New- 
foundland on  the  north.  It  carries  varying  quantities  of  gold. 
The  richest  portion  is  in  the  southern  part  of  the  belt.  Hundreds 
of  samples  from  this  belt  have  shown  traces  of  gold  in  almost  all 
cases.  In  the  northern  portion  of  the  belt,  at  Newport,  Vermont, 
samples  from  Cambrian  sericite  schists  have  contained  over  $20 
in  gold  per  ton  of  ore.  Near  Lisbon,  N.  H.,  is  found  the  best  rep- 
resentative of  gold  deposits  in  the  northern  half  of  the  belt. 
Samples  containing  more  than  $500  in  gold  per  ton  have  been 
assayed.  A  small  mill  is  treating  some  of  the  ore  but  the  output 
is  small.  The  ore  occurs  in  a  fissure  vein  traversing  the  crystal- 
line rocks.  The  gangue  is  quartz,  and  in  the  upper  portion  of  the 
lode  the  associated  pyrite  has  suffered  much  oxidation. 

The  Southern  Appalachian  Field :     The  gold  fields  of  the  South- 


PRECIOUS  METALS  61 

ern  Appalachians  are  situated  in  an  area  of  crystalline  rocks  whose 
general  strike  is  northeast  and  southwest.  The  auriferous  rocks 
consist  of  granites,  gneisses,  schists,  slates  and  shales.  The 
auriferous  quartz  veins  coincide  imperfectly  with  the  dip  and 
strike  of  the  strata. 

In  Alabama  there  are  3500  square  miles  of  auriferous  crystal- 
line rocks  in  Chambers,  Chilton,  Clay,  Cleburne,  Coosa,  Elmore, 
Randolph,  Talladega  and  Tallapoosa  Counties.  The  gold  is 
encased  in  glassy  quartz  associated  mainly  with  pyrite. 

In  Georgia  the  auriferous  belt  extends  in  a  northeasterly 
direction  across  the  entire  state.  The  associated  rocks  are  sheared 
acid  and  basic  intrusives.  Certain  bands  of  gneisses  and  am- 
phibolites  have  been  produced  in  the  shearing,  and  their  fissures 
are  filled  with  auriferous  quartz  associated  with  pyrite. 

The  southern  Appalachian  gold  field  reaches  its  maximum  im- 
portance in  the  Carolinas.  From  the  northern  part  of  South 
Carolina  it  extends  across  the  entire  state  of  North  Carolina  in  a 
northeasterly  direction  to  Virginia.  It  has  a  maximum  width  of 
50  miles,  and  is  flanked  upon  the  west  by  an  extensive  granitic 
area  and  upon  the  cast  by  Jura-Trias  terranes.  The  gold  occurs 
in  fissure  veins  with  a  quartz  gangue,  and  as  pyritic  impregnation 
deposits  with  irregular  and  lenticular  quartz  intercalations  in  the 
schists  and  slates. 

The  age  of  these  ores  is  in  all  probability  Algonkian  for  their 
deposition  took  place  subsequent  to  the  development  of  the  schis- 
tosity  of  the  Algonkian  slates.  The  gold  in  the  Jura-Trias 
conglomerate  must  have  been  pre-Jura-Triassic. 

The  South  Mountain  belt  is  situated  in  the  western  part  of 
North  Carolina.  The  principal  mining  region  is  25  miles  long 
and  about  12  miles  wide.  The  terranes  are  chiefly  bio  tit  e 
schists  and  hornblende  gneisses.  The  schists  are  regarded  as 
metamorphosed  granites  and  diorites.  They  are  often  garnetif- 
erous  and  of  special  interest  as  they  bear  the  rare  minerals 
ziroon,  monazite  and  xenotime.  The  strike  of  these  terranes 
is  northeasterly  and  their  dip  is  about  25°.  The  gneisses 
contain  isolated  masses  of  pyroxenite  and  amphibolites  often 
metamorphosed  into  talc  and  serpentine. 

The  auriferous  quartz  veins  are  noted  for  their  remarkable 
regularity.  Their  general  strike  is  N.  60°  to  N.  70°  E.  and  dip  at 
a  steep  angle  to  the  northwest.  The  veins  are  exceedingly  narrow 
averaging  less  than  6  in.  The  gangue  is  usually  a  milky 


62  ECONOMIC  GEOLOGY 

quartz  and  somewhat  cellular  from  the  oxidation  of  pyrite.  The 
veins  were  filled  from  ascending  gold-bearing  solutions.  The 
pyrite  would  serve  as  a  reducing  agent  for  the  gold  thus  held  in 
solution. 

The  principal  mining  ground  is  in  placers  which,  according  to 
E.  T.  Hancock,  may  be  divided  into  three  classes.  (1)  The 
gravel  of  the  stream  and  bottom  lands,  deposited  by  fluviatile 
action.  (2)  The  gulch  and  hill-side  deposits  or  accumulations 
due  to  disintegration  and  motion  induced  by  frost  action  and 
gravity.  (3)  The  upper  decomposed  layers  of  the  country  rocks 
in  place. 

The  Virginia  belt  extends  from  North  Carolina  in  a  northeast- 
erly direction  to  Montgomery  County,  Maryland,  and  is  from 
10  to  20  miles  in  width.  The  terranes  consist  largely  of  mica 
schists  and  gneisses,  often  garnetiferous,  talcose  and  chloritic. 
The  auriferous  veins  conform  largely  to  dip  and  strike  of  the 
schists.  They  are  very  irregular,  lenticular  and  narrow,  seldom 
exceeding  a  few  feet  in  width.  The  chief  gangue  is  quartz  but 
the  wall  rocks  are  often  impregnated  with  auriferous  pyrite. 
The  Fisher  lode  in  Louisa  County  is  the  most  persistent.  This 
lode  has  been  opened  for  a  distance  of  more  than  5  miles, 
but  the  maximum  depth  to  which  the  lode  has  been  worked  is 
approximately  250  ft. 

Black  Hills  District. — The  Black  Hills  are  situated  in  Lawrence 
County  in  the  western  part  of  South  Dakota.  The  auriferous 
ores  are  in  the  northern  Black  Hills.  The  gold  of  South  Dakota 
was  first  discovered  in  the  placers  which  occupy  depressions  in  the 
pre-Cambrian  schists.  The  region  in  one  of  peculiar  interest  for 
it  represents  some  of  the  earliest  known  and  worked  placers  of  the 
United  States.  After  the  placers  became  somewhat  exhausted  at 
the  surface,  the  workings  were  carried  downward  into  the  con- 
glomerate that  marks  the  base  of  the  Cambrian  series  of  rocks. 

Some  geologists  are  of  the  opinion  that  the  origin  of  the  placer 
gold  is  from  the  reefs  formed  by  the  Homestake  ledge  in  the 
Cambrian  Sea.  Other  geologists  consider  that  the  gold  was 
chemically  precipitated  by  the  action  of  the  sulphides  of  iron  and 
therefore  not  a  true  detrital  deposit.  A  reason  for  this  conclusion 
lies  in  the  fact  that  the  matrix  of  the  auriferous  conglomerate  is 
pyrite  rather  than  quartz;  also  that  the  gold  occurs  along  frac- 
ture planes  stained  by  iron  oxides. 

Homestake  District :     The  Homestake  belt  is  the  most  impor- 


PRECIOUS  METALS  63 

tant  field  in  the  Black  Hills.  It  has  been  a  steady  producer  of  gold 
for  many  years.  The  Homestake  ore  bodies  occur  in  the  Algonkian 
slates  which  are  for  the  most  part  of  sedimentary  origin.  One 
variety  has  howev-er  been  recognized  as  a  metamorphosed  igneous 
rock  and  catalogued  as  an  amphibolite  because  amphibole  is  the 
most  prominent  constituent.  The  amphibolites  occur  as  dikes  or 
irregular  masses  in  the  other  Algonkian  rocks.  The  associated 


FIG.  45. — Banded  siliceous  ore  in  No.  2  shaft  Union  mine,  Black  Hills 
district,  South  Dakota,  showing  preservation  of  sedimentary  bedding  in 
the  ore,  the  banding  being  continuous  with  the  inclosing  stratified  rocks. 
(After  J .  D.  Irving,  U.  S.  Geological  Survey.) 

metamorphosed  sediments  are  quartzites,  quartz-schists,  mica- 
schists,  phyllites  and  graphitic,  garnetiferous  and  chloritic  slates. 
More  recent  eruptives  cut  through  all  these  rocks  as  well  as 
the  ore  bodies  themselves.  The  later  eruptives  are  of  two  types. 
(1)  A  rhyolite  porphyry,  which  is  by  far  the  most  common  rock. 
It  not  only  cuts  through  the  Algonkian  terranes  but  spreads  out 
in  sheets  or  sills  in  the  nearly  horizontal  strata  of  the  overlying 
Cambrian  series.  (2)  The  second  eruptive  is  a  trachytoid  phono- 


64  ECONOMIC  GEOLOGY 

lite  which  appears  at  the  800-ft.  level  of  the  Homestake  mine  and 
is  a  common  rock  in  various  parts  of  the  northern  Black  Hills 
(Fig.  45). 

According  to  J.  D.  Irving,  the  ores  of  the  Homestake  zone  are 
poorly  denned  masses  of  rock  sufficiently  impregnated  with  gold 
to  pay  for  working,  but  otherwise  hardly  to  be  distinguished  from 
the  country  rock  in  which  they  occur.  They  are  singularly  bar- 
ren of  the  usual  ore  minerals.  The  gold  occurs  in  so  finely  divided 
a  state  that  the  particles  are  invisible  even  with  a  magnifying 
glass.  Leaf  gold  has,  however,  been  found  but  without  evidence 
of  crystalline  structure.  Pyrite  and  arsenopyrite  are  the  only 
other  metallic  minerals  present.  The  former  is  more  abundant. 

Quartz  is  the  most  abundant  gangue  mineral.  It  occurs  in 
veins  or  lens-shaped  masses  often  of  considerable  size  and  of  sev- 
eral different  periods  of  formation.  Calcite  and  dolomite  are 
also  present  as  gangue  minerals  usually  of  secondary  origin,  but 
not  universally  present. 

Origin  of  The  Homestake  Ores :  There  is  no  definite  evidence  as 
to  the  source  of  the  gold  and  pyrite.  Irving  considers  them  to 
have  been  leached  from  the  rocks  at  some  distance  below  the  sur- 
face by  percolating  waters  and  to  have  been  precipitated  in  con- 
tact with  graphitic  matter  and  possibly  also  with  original  pyrite, 
present  in  the  slates. 

A  second  period  of  mineralization  came  after  the  later  intrusion 
of  the  rhyolite  porphyry,  followed  the  same  general  channels  and 
deposited  the  gold  and  pyrite.  This  intrusive  did  not  stop  at  the 
Cambrian  contact,  but  continued  on  through  cracks  and  fissures 
into  the  Cambrian  rocks  and  deposited  gold  and  pyrite  abun- 
dantly in  the  basal  conglomerate  of  the  Cambrian  series  and  in 
the  calcareous  terranes  immediately  overlying  the  outcrop  of  the 
Homestake  belt.  In  the  conglomerate,  wolframite  replaces  some- 
what, the  pyrite  but  there  is  no  evidence  of  pneumatolytic  action. 

The  secondary  enrichment  of  the  ores  by  surface  leaching  has 
been  of  relatively  small  importance.  There  is  little  evidence  of 
decrease  in  value  of  ore  with  depth.  In  fact  the  size  of  the  ore 
body  appears  to  be  increasing  rather  than  decreasing  with  descent. 
The  ore  as  a  whole  averages  between  $5  and  $6  per  ton. 

According  to  J.  D.  Irving,  the  ore  occurs  in  three  distinct  var- 
ieties. (1)  Banded  ore:  That  is,  ore  wherein  the  mineralization 
has  not  been  accompanied  by  distortion  of  the  original  structures 
of  the  rock.  (2)  Contorted  ore:  That  is,  ore  where  the  original 


PRECIOUS  METALS 


65 


66 


ECONOMIC  GEOLOGY 


rock  has  undergone  very  great  distortion.  (3)  Massive  ore: 
Where  few,  if  any,  traces  of  either  the  original  structure  or  the 
original  constituents  of  the  Algonkian  rocks  can  be  observed. 

Cordilleran  Region. — This  vast  area  stretches  through  British 
Columbia  on  the  north  southward  to  Mexico  and  includes  prac- 
tically all  States  traversed  by  the  Rocky  Mountains.  Its  best 
development  is  in  Colorado.  Each  of  these  western  States  is 
subdivided  into  fields  and  districts,  and  each  is  worthy  of  a  de- 
tailed description  but  only  a  few  of  the  most  important  fields  are 
considered. 

Cripple  Creek.  This  district  is  situated  10  or  12  miles  from 
Pikes  Peak,  Colorado,  but  in  the  foot  hills  of  the  same  mountain 


FIG.  47. — Small  vein  of  andesitic  breccia,  Independence  mine,  Cripple 
Creek,  Colorado.  An,  Andesitic  breccia;  P,  pyrite;  F,  fluorite;  Q,  quartz; 
V,  valencianite.  (After  W.  Lindgren,  U.  S.  Geological  Survey.) 

mass.  The  field  is  the  most  important  as  a  gold  producer  in  the 
Cordilleran  belt.  Its  importance  is  testified  to  by  the  fact  that 
it  has  already  produced  more  than  $200,000,000  in  gold.  It  is 
essentially  a  gold  field  for  the  ore  contains  from  1  to  10  oz. 
of  silver  per  ton. 

The  district  consists  of  a  series  of  highly  metamorphosed  mica 
schists  bearing  sillimanite,  of  pre-Cambrian  age;  the  Pikes  Peak 
granite,  characterized  by  its  microcline;  the  Cripple  Creek  granite 
also  bearing  microcline;  and  the  Spring  Creek  granite  which  carries 
the  commonest  of  the  feldspars,  orthoclase.  In  the  metamor- 
phics  there  also  appear  some  differentiation  products  of  an  olivine- 
syenite  magma.  The  volcanics  of  the  area  consist  largely 


PRECIOUS  METALS 


67 


of  tuffs  and  breccias  of  Tertiary  age.  These  are  cut  by  dikes  of 
phonolite,  latite-phonolite,  syenite,  dolorite,  and  even  the  more 
basic  rocks.  (See  Fig.  46.) 

The  ore  bodies  occur  in  two  forms.  (1)  Lodes  or  veins,  and 
(2)  irregular  replacement  deposits.  The  veins  are  exceedingly 
narrow  fissures  incompletely  filled.  They  are  essentially  in  the 
volcanics  and  present  a  radical  appearance.  They  are  short  and 
nearly  vertical  (Fig.  47).  Some  of  the  most  productive  fissures 
have  been  only  a  few  hundred  feet  in  length.  In  fact  the  entire 
field  is  circular  in  form  with  a  radius  of  2  or  3  miles. 

The  lodes  may  occur  in  both  the  eruptives  and  the  irruptives. 


Scale 

10 


20  feet 


FIG.  48. — Sheeted  zone  and  flats  of  the  Apex  vein,  Ajax  mine,  Cripple 
Creek  district,  Colorado.  (After  W.  Lindgren  and  F.  L.  Ransome,  U.  S. 
Geological  Survey.) 

In  the  former  case  they  favor  the  breccias  and  in  the  latter  the 
granites,  as  shown  in  Fig.  48.  The  fissures  seem  to  have  been 
formed  by  compressive  stresses  associated  with  the  cooling  igneous 
rocks.  The  fissures  are  particularly  small  and  narrow  and  may 
occur  in  any  rock  in  the  series.  (See  Fig.  49.) 

The  replacement  deposits  usually  occur  in  the  granite.  The 
principal  gold  ore  is  the  telluride,  petzite  or  calaverite  which 
upon  roasting  brings  the  gold  to  the  surface  forming  beautiful 
museum  specimens.  Pyrite  is  associated  with  the  tellurides. 
Near  the  surface  and  in  the  oxidized  zone  in  general  the  gold 
appears  as  brown,  spongy  gold  while  the  tellurium  has  been  con- 
verted into  tellurites. 

The  common  gangue  minerals  are  quartz,  fluorite  and  dolomite 


68 


ECONOMIC  GEOLOGY 


with  the  sulphides  of  lead,  zinc,  antimony  and  molybdenum  spar- 
ingly present.  The  ores  were  deposited  from  hot  alkaline  solu- 
tions. Fluorine  was  an  important  mineralizer.  The  rich  tellu- 
ride  ore  is  shipped  to  Pueblo  for  smelting,  while  the  lower  grades 
are  chlorinated  or  cyanided  at  the  mines  (Fig.  50) .  The  banner 
production  of  this  small  area  was  reached  in  1900  when  an  out- 
put of  more  than  $18,000,000  was  credited  to  the  district,  but 
the  output  has  since  declined  to  nearly  $10,000,000  per  annum. 
San  Juan  District:  The  San  Juan  mining  belt  covers  a  large 


a  b  a  b  a 


E 


FIG.  49. — Section  in  the  Victor, 
Smuggler  Lee,  and  Buena  Vista  mines, 
Cripple  Creek  district,  Colorado,  showing 
the  parallel  ore  bodies  A .  (After  Penrose.) 


FIG.  50.— Section 
showing  the  forms  of  the 
veins  in  the  Blue  Bird 
mine,  Cripple  Creek  dis- 
trict, Colorado,  a,  Ore; 
b,  country  rock.  (After 
Penrose.) 


area  of  mountainous  territory  in  the  southwestern  part  of  Colo- 
rado. It  embraces  the  counties  of  Dolores,  Hinsdale,  La  Plata, 
Ouray,  San  Juan  and  San  Miguel.  The  continental  divide 
traverses  the  area  with  several  peaks  surpassing  14,000  ft.  in 
altitude.  The  base  of  the  geological  series  is  Archean.  The  over- 
lying Tertiary  sedimentaries  are  capped  with  andesites,  diabases, 
diorites,  etc.  Masses  of  rock  composed  of  volcanic  ejectamenta 
are  not  infrequent.  Many  V-shaped  valleys  of  incision  traverse 
the  area.  The  whole  field  presents  the  appearance  of  a  deeply 
cut  volcanic  plateau. 


PRECIOUS  METALS  69 

Telluride  District :  In  the  vicinity  of  Telluride  there  is  a  very 
interesting  development  of  veins.  The  Smuggler  vein  is  very 
persistent.  It  is  definitely  known  that  it  extends  four  miles 
across  the  high  divide  that  separates  the  Marshall  basin  from 
the  valleys  of  Canon  Creek.  Many  of  the  veins  consist  of  closely 
spaced  fissures  filled  with  ore.  The  pay  portion  rarely  comprises 
the  entire  vein  but  rather  forms  a  narrow  strip  following  either 
the  hanging  wall  or  the  footwall.  The  gold  is  often  encased  in 
pyrite  and  chalcopyrite  with  quartz  gangue.  The  silver  is  in  the 
galenite  and  freibergite,  but  the  double  sulphides  of  silver  with 
antimony  and  arsenic,  as  polybasite,  stephanite  and  proustite 
are  known.  According  to  F.  L.  Ransome  the  downward  percola- 
tion of  meteoric  waters  dissolved  the  alkalis  from  the  andesites  and 
rhyolites  as  sulphides.  These  solutions  rose  in  temperature  as 
they  approached  the  magma  and  became  charged  with  sulphuric 
and  carbonic  .acids  derived  from  volcanic  sources.  These  acids 
gathered  the  metals  and  their  gangue  minerals  from  the  more 
basic  material  and  while  penetrating  the  open  spaces  of  the  fis- 
sured zone,  deposited  the  metals  and  gangue  minerals  at  higher 
altitudes.  The  carbonates  were  deposited  upon  the  walls  of  the 
fissures  while  the  gold,  to  some  extent,  penetrated  the  walls. 

Silverton:  The  Silverton  district  lies  to  the  east  of  the  Tellu- 
ride. The  Tertiary  volcanics  are  separated  from  the  Carbon- 
iferous terranes  by  a  conglomerate.  According  to  H.  Ries,  the 
ore  depoits  fall  into  three  classes.  (1)  Lodes,  which  include 
most  of  the  known  productive  deposits,  (2)  stocks,  which  in- 
clude most  of  the  ore  bodies  formally  worked  on  Red  Mountain, 
and  (3)  metasomatic  replacements,  which  comprise  a  few  de- 
posits in  the  limestones  or  rhyolites. 

The  lodes  occur  in  all  terranes  from  the  pre-Cambrian  to  the 
Tertiary  irruptives. 

The  Tertiary  fissuring  is  most  pronounced  in  a  northeast  and 
southwest  direction.  The  lodes  are  simple  fissure  veins.  Some- 
times these  veins  bear  both  native  gold  and  silver.  The  gold  is 
often  encased  in  chalcopyrite  and  the  silver  in  galenite,  tetrahe- 
drite  and  enargite.  The  common  gangue  minerals  are  quartz  and 
calcite.  The  ores  were  deposited  from  hot  ascending  solutions 
with  depth  of  origin  unknown. 

Ouray  District :  The  Ouray  district  surrounds  the  picturesque 
city  of  Ouray.  The  terranes  comprise  limestones,  conglomerates 
quartzites,  sandstones  and  shales  overlain  by  Tertiary  volcanics. 


70  ECONOMIC  GEOLOGY 

Fissure  veins  are  the  most  pronounced  and  persistent  type  of  ore 
deposits  in  the  district.  Some  of  these  may  be  traced  for  more 
than  a  mile  along  the  line  of  their  outcrop.  Sometimes  they  reach 
a  width  of  75  to  100  ft.  and  are  well  mineralized  throughout. 
Much  free  gold  occurs  in  the  Camp  Bird,  Revenue  Tunnel,  Atlas 
and  Torpedo-Eclipse  mines.  Samples  from  the  latter  mine  have 
assayed  over  $50,000  per  ton.  The  ore  is  often  associated  with 
tellurium  also  encased  in  chalcopyrite  with  a  gangue  of  country 
rock  and  clay. 

Quartz,  calcite,  fluorite  and  bariteare  common  gangue  minerals. 
The  silver  occurs  in  part  native,  in  part  with  galenite  and  tetra- 
hedrite  and  in  part  as  stephanite.  Less  important  replacement 
deposits  occur  in  the  quartzites,  sandstones  and  limestones. 
These  deposits  in  the  sandstones  are  more  or  less  irregular  but  in 
the  limestones  they  occur  as  broad  flat  ore  bodies  associated  with 
the  fissure  veins  that  penetrate  the  limestones. 

The  fissuring  appears  to  be  late  Tertiary  and  the  mineralization 
in  some  period  later  than  the  introduction  of  the  volcanics. 

Georgetown  District:  This  district  is  in  the  Continental 
Range  in  Clear  Creek  County,  about  50  miles  west  of  Denver. 
The  base  of  the  Geological  series  consists  of  pre-Cambrian  schists 
of  sedimentary  origin  which  are  overlain  by  highly  metamor- 
phosed schistose  rocks  of  igneous  origin.  This  series  of  terranes 
was  later  penetrated  by  both  acid  and  basic  intrusives.  The  latest 
irruptives  of  probably  late  Cretaceous  or  Tertiary  age,  consist  of 
porphyry  dikes.  These  porphyries  are  of  special  interest  because 
they  stretch  in  a  northeasterly  and  southwesterly  direction  nearly 
the  entire  length  of  the  state.  The  lodes  occur  in  fissure  veins 
that  cut  the  pre-Cambrian  schistose  rocks. 

Auriferous  pyrite  with  a  quartz  gangue  predominates  in  the 
neighborhood  of  Georgetown.  These  veins  may  or  may  not  bear 
silver.  At  the  Silver  Plume  mine  much  fine-grained  argentiferous 
galenite  is  encountered.  At  Idaho  Springs  the  prevailing  ore  is 
an  argentiferous  galenite-sphalerite  which  contains  but  little  gold. 
According  to  J.  E.  Spurr,  descending  meteoric  waters  have 
effected  from  the  wall  rock  a  mixture  of  quartz,  calcite,  kaolin 
and  sericite.  The  walls  of  the  fissure  appear  to  have  been  the 
source  of  the  gangue  minerals,  while  the  gold  and  silver  were 
contributed  to  the  veins  by  magma  tic  waters. 

The  gold-bearing  veins  appear  at  the  lower  level  and  the  silver 
at  the  higher  altitudes  in  this  deeply  incised  region.  The  former 


PRECIOUS  METALS 


71 


72  ECONOMIC  GEOLOGY 

metal  therefore  is  found  most  abundantly  in  what  may  be  only 
the  lower  portions  of  the  argentiferous  veins. 

Sierra  Region:  Goldfield  is  situated  in  the  southwestern  part 
of  Nevada  in  Esmeralda  County.  (See  Fig.  51.)  According 
to  F.  L.  Ransome  the  base  of  the  geological  series  consists  of  pre- 
Cambrian  metamorphics.  These  suffered  denudation  until  the 
close  of  the  Jurassic  Age,  when  the  intrusive  alaskite  and  granite 
were  introduced.  This  was  followed  in  Tertiary  time  by  eruptives 
ranging  from  rhyolite  to  basalt.  The  dacite  is  the  most  produc- 
tive extrusive,  while  some  rich  ores  are  found  in  the  andesites. 
The  ore  bodies  are  noted  for  their  remarkable  richness  and  irregu- 
larity. The  fissures  are  usually  irregular,  small  and  intersecting 
fracture-flows  passing  into  brecciated  material.  Faulting  seems 
to  be  absent.  After  the  dacite  lode  solidified  unknown  stresses 
developed  this  intricate  fracturing.  The  ores  are  free  gold  and 
auriferous  pyrite  associated  with  silver,  copper,  antimony,  arsenic, 
bismuth  and  tellurium  minerals.  Magmatic  waters  contributed 
the  gold  to  the  fissures.  These  ascending  solutions  bore  H2S 
and  CC>2  Near  the  surface  the  hydrogen  sulphide  was  in  part 
oxidized  to  H2SO4-  The  downward  trend  of  these  acid  solutions 
through  the  shattered  dacites  and  andesites  and  their  subsequent 
mingling  with  ascending  solutions  caused  the  precipitation  of 
their  metallic  contents.  The  gold  would  be  precipitated  by  alka- 
line carbonates,  as  native  gold.  The  freshly  formed  pyrite  would 
serve  as  a  reducing  agent  upon  its  encased  gold.  A  second  stage 
of  fracturing  and  mineralization  seems  to  have  occurred  in  this 
field  (Figs.  52  and  53). 

Comstock  Lode:  The  Comstock  Lode  is  situated  in  the  south- 
western part  of  Nevada  on  the  eastern  flank  of.  Mt.  Davidson  in 
the  vicinity  of  Virginia  City,  Washoe  County.  The  geology  of 
this  region  has  been  a  matter  of  much  study  on  the  part  of  able 
scientists  like  Becker,  Von  Richthofen,  Hague  and  Iddings.  Von 
Richthofen  considered  the  ore  body  as  filling  a  fissure  on  the 
contact  between  a  syenite  foot-wall  and  an  eruptive  propylite 
hanging  wall  (Fig.  54). 

Clarence  King  considered  that  the  vein  filled  a  fissure  between 
a  syenite  and  the  Tertiary  eruptives  poured  out  upon  the  flank 
of  Mt.  Davidson.  Arnold  Hague  and  J.  P.  Iddings,  from  an  exten- 
sive study  of  the  rock  masses,  concluded  that  the  Comstock  Lode 
occupies  a  line  of  faulting  rocks  of  the  Tertiary  age  and  cannot  be 
considered  as  a  contact  vein  between  two  different  rock  masses. 


PRECIOUS  METALS 


73 


74 


ECONOMIC  GEOLOGY 


I 

cf 


O 

O 


PRECIOUS  METALS 


75 


The  vein  itself  is  a  true  fissure  vein  about  4  miles  long,  and 
several  hundred  feet  wide,  branching  in  the  upper  portions,  and 
faulted  3000  ft.  in  the  center.  The  faults  gradually  die  out  as  the 
ends  of  the  veins  are  reached.  The  lode  contains  gold  and  silver 
and  the  chief  gangue  mineral  is  quartz.  According  to  Von 
Richthofen,  the  ores  and  gangue  minerals  were  brought  up  by 
ascending  solutions.  Fluorine,  chlorine  and  sulphur  were  the 
agents  of  solution. 

The  ore  occurs  in  bonanzas  of  remarkable  richness.  One  of 
these  bonanzas  is  said  to  have  furnished  $110,000,000  in  gold  and 
silver.  The  ores  are  marked  also  by  great  irregularity.  Gold  pre- 
dominates over  silver  in  the  ratio  of  3  : 2.  The  mine  has  yielded 
nearly  $400,000,000  and  is  still  a  steady  producer  (Fig  55). 


FIG.  54.— East-west  section  through  the  Comstock  lode  in  Nevada  showing 
the  position  of  two  of  the  ore  bodies,  and  of  the  Sutro  tunnel. 

The  Pacific  Coast  Region. — This  belt  extends  along  the  Pacific 
coast  from  Lower  California  northward  through  California, 
Oregon,  Washington  and  British  Columbia.  The  California 
field  is  the  most  important  of  all  for  it  furnishes  an  annual  out- 
put of  approximately  $20,000,000.  The  belt  is  characterized  by 
quartzose  ores  and  auriferous  sulphides.  In  the  more  northerly 
portion  of  the  belt  silver  occurs  with  the  gold  and  the  auriferous 
sulphides  are  without  free  gold.  The  region  is  characterized  by 
many  placers  which  have  been  derived  from  the  weathering  of 
the  upper  portions  of  the  quartz  veins  (Fig.  56). 

The  Mother  Lode  Belt:  This  belt  comprises  a  large  series  of 
quartz  veins  stretching  in  a  northerly  and  southerly  direction  for 


76 


ECONOMIC  GEOLOGY 


FIG.  55. — View  of  a  portion  of  Mercur,  Utah,  and  the  Mercur  mine.     (By 
permission   of    the   Macmillan   Company,  from   Ries'    Economic    Geology.) 


FIG.  56. — Lowest  bed  of  coarse  and  bouldery  gold-bearing  gravel  at 
Cherokee  mine,  Butte  County,  California.  (After  W.  Lindgren,  U.  S. 
Geological  Survey.} 


PRECIOUS  METALS  77 

113  miles.  The  mines  are  situated  in  Amador,  Calaveras,  El 
Dorado,  Mariposa  and  Tuolumne  Counties.  These  counties 
furnish  three-fourths  of  the  milling  ores  of  the  State.  The  aver- 
age recovery  per  ton  is  much  less  than  in  other  counties  where  the 
veins  are  smaller  and  richer.  The  average  recovery  from  all  the 
counties  in  the  Mother  Lode  district  is  less  than  $4  per  ton  while 
in  Nevada  County  the  amount  exceeds  $10  in  gold  and  silver  per 
ton  of  ore  mined. 

One  characteristic  of  the  Mother  Lode  is  the  permanancy  of 
the  ore  with  increasing  depth.  In  Amador  County  the  mines 
are  now  3500  ft.  deep  and  the  ore  is  as  good  as  that  found  at  the 
surface.  The  ores  occur  in  fissure  veins  in  steeply  dipping  slates 
and  altered  volcanics  of  Carboniferous  and  Jurassic  age.  The 
ores  are  found  at  so  great  a  distance  from  the  granitic  rocks  of  the 
Sierra  Nevadas  that  they  are  supposed  to  bear  no  genetic  rela- 
tion to  them.  The  veins  occur  both  in  the  slates  and  at  their 
contact  with  diabase  dikes.  The  veins  show  a  remarkable  ex- 
tent and  uniformity.  In  the  tilted  layers  of  the  slate  there  lay 
planes  of  weakness  which  the  mineral-bearing  solutions  followed. 
The  chief  gangue  mineral  is  quartz,  and  the  ore  is  native  gold  and 
auriferous  pyrite. 

Nevada  County:  The  Grass  Valley  district  of  Nevada  County 
still  continues  to  be  the  leading  quartz- mining  section  of  the  State. 
None  of  the  other  counties,  even  those  of  the  famous  Mother 
Lode,  approach  it  in  its  production  of  gold.  The  deep  mines  of 
the  county  are  yielding  per  annum  about  2,000,000  tons  of  free 
milling  ores  and  500,000  tons  of  auriferous  copper  ores  that  are 
treated  at  the  smelters.  The  veins  are  quartz  and  occur  along 
the  contact  between  a  grano-diorite  and  diabase  prophyry.  They 
also  cut  the  igneous  rocks.  Two  systems  of  fissuring  are  known. 
The  gold  is  either  native  or  associated  with  metallic  sulphides. 
The  width  of  the  vein  seldom  exceeds  3  ft.  The  lode  ore  oc- 
curs in  well-defined  bodies  or  pay  shoots.  W.  Lindgren  believes 
that  the  ores  were  leached  out  of  the  rock  at  a  considerable  depth 
and  deposited  by  hot  solutions  while  the  wall  rocks  contained 
the  rare  metals  in  a  disseminated  condition. 

The  Alaska  Field. — The  region  may  be  divided  into:  (1)  The 
Sitka  district;  (2)  the  Juneau  and  Douglas  Island  district  North- 
east of  Sitka;  (3)  the  Fairbanks  district  in  the  central  part  of 
Alaska  and;  (4)  the  Seward  Peninsula  in  the  western  part  of 
Alaska,  as  shown  in  Fig.  57. 


78 


ECONOMIC  GEOLOGY 


•  Gold  placers 
-fGold  and  silver  lodes 
D  Copper 

+Tln  lode* 
/X  Tin  placer. 

•  Coal 

e  Petroleum 


FIG.    57. — Map   showing   mineral   deposits   of   Alaska.     After   Brooks. 
(By  permission  of  the  Macmillan  Company,  from  Ries'  Economic  Geology.) 


Cabbro  A/bite  Diorite          Slate 

traversed  by  veins  of 


ra  versed  by  veins 
Ca/cife  d  .Ouartf 

FIG.  58. — Gold  ore  in  transverse  veins  in  the  Ready  Bullion  mine,  Tread- 
well,  Alaska.     (After  A.  C.  Spencer,  U.  S.  Geological  Survey.) 


PRECIOUS  METALS 


79 


It  is  of  interest  to  note  that  the  United  States  paid  $7,200,000 
for  the  Alaskan  territory.  It  was  catalogued  as  the  "  white 
elephant"  on  the  hands  of  the  United  States  government.  Yet 
the  total  gold  brought  out  of  Alaska  exceeds  $150,000,000  with 
an  output  in  1910  of  $20,947,600  or  nearly  three  times  the 
amount  paid  for  the  territory. 

The  Lodes:  Gold  quartz  lodes  occur  most  abundantly  along 
the  coast,  especially  near  Sitka  and  on  Douglas  Island.  The 
ore  bodies  are  dikes  of  diorite  traversing  black  slates.  The  hang- 
ing wall  of  the  ore  body  is  a  much  altered  intrusive  greenstone 
and  the  foot  wall  is  a  black  slate.  (See  Fig.  58.) 


Treadwell  Mine 


FIG.  59. — Section  through  the  Alaska  Treadwell  mine,   Douglas  Island, 
near   Juneau,    Alaska. 

Two  sets  of  fractures  at  right  angles  to  each  other  seem  to 
have  been  incident  to  the  epirogenic  movements  of  the  region. 
According  to  Spencer,  the  mineralization  was  caused  by  hot  as- 
cending solutions  of  magmatic  origin.  Secondary  concentra- 
tion is  not  in  evidence.  The  actual  depth  to  which  the  ores  can 
be  worked  depends  more  upon  the  increased  cost  of  mining  at 
great  depths  than  upon  the  exhaustion  of  the  ore  body.  An 
almost  continuous  ore  body  has  been  developed  for  more  than 
half  a  mile.  (See  Fig.  59.) 

The  Placers:  Gold  occurs  most  abundantly  in  Alaska  in 
placers.  The  placer  deposits  of  Seward  Peninsula  alone  are  about 
equal  in  area  to  those  of  California  and  approximately  ten  times 


80  ECONOMIC  GEOLOGY 

as  large  as  those  of  the  Klondike  field  which  lies  east  of  the  Inter- 
national boundary.  Mining  in  Klondike  is  said  to  have  passed 
its  zenith  while  the  maximum  yearly  output  of  Seward  Peninsula 
is  still  to  be  reached.  The  Klondike  placers  were  discovered  in 
1896  and  those  on  the  Seward  Peninsula  in  1897. 

According  to  A.  H.  Brooks,  three  conditions  are  usually  opera- 
tive in  the  formation  of  placers:  (1)  The  occurrence  of  gold  in 
bed  rock  to  which  erosion  has  access;  (2)  the  separation  of  gold 
from  bed  rock  by  weathering  or  abrasion;  and  (3)  the  transporta- 
tion, sorting  and  deposition  of  the  weathered  and  eroded  auriferous 
material. 

Origin:  In  some  parts  of  Europe,  in  the  tropics  and  in  the 
southern  Appalachians  some  workable  placers  have  been  formed 
solely  by  the  weathering  of  the  bed  rock  in  place.  T.  A.  Rickard 
recognized  placers  in  Australia  that  have  been  concentrated 
through  the  agency  of  the  wind,  the  lighter  material  having  been 
removed.  In  the  formation  of  the  true  placers  transportation, 
sorting,  and  deposition  of  material  furnished  by  the  weathering 
of  the  rocks  are  important  agents.  Uplift  may  revive  the  forces 
of  erosion  and  render  these  agencies  repeatedly  effective,  which 
results  in  the  reconcentration  of  the  alluvial  gold. 

The  classification  of  placers  should  be  based  both  upon  origin 
and  form.  According  to  their  origin  there  are  three  types  of 
placers:  (1)  Residual;  (2)  sorted  placers;  and  (3)  re-sorted  placers. 
The  residual  placers  are  those  in  which  there  has  been  no  water 
transportation,  the  concentration  of  gold  being  due  solely  to  rock 
weathering.  The  gold  of  the  sorted  placers  is  the  result  of  trans- 
portation, sorting  and  deposition  of  auriferous  material  by  water. 
Re-sorted  placers  are  those  in  which  the  gold  has  passed  through 
two  or  more  cycles  of  erosion  before  its  final  deposition. 

Residual  placers  are  practically  all  of  one  type.  Sorted  placers 
may  be  subdivided  into  hillside,  creek  and  gulch,  river  bar,  gravel 
plain,  bench  and  high  bench  deposits.  Re-sorted  placers  may  be 
divided  into  creek  and  gulch,  beach  and  elevated  beach  deposits. 
Intermediate  types  may  be  found  which  belong  to  either  one  of 
the  last  two  groups.  Hillside  placers  occur  on  hill  slopes  and 
do  not  occupy  any  well-defined  channels.  They  grade  on  the  one 
hand  into  placers  of  residual  origin  and  on  the  other  into  placers 
of  the  stream  or  gulch  type.  Creek  and  gulch  placers  occur 
both  in  material  that  has  been  assorted  once  and  in  that  which 
has  passed  through  several  cycles  of  erosion. 


PRECIOUS  METALS  81 

Gold  in  the  Placers:  The  gold  has  usually  been  deposited 
where  the  current  of  a  stream  has  been  checked.  A  broad  basin 
above  a  steep-walled  canyon  is  more  likely  to  carry  gold  than  the 
valley  below  the  canyon,  provided  the  bed  rock  source  of  the  gold 
is  above  the  basin.  Coarse  gold  is  more  likely  to  be  found  at  the 
head  of  a  filled  basin  than  near  its  outlet.  The  same  holds  true 
of  a  stream  that  debouches  on  a  coastal  plain  which  will  deposit 
the  coarse  gold  it  may  carry  near  the  head  of  its  delta. 

A.  J.  Collier  and  F.  L.  Hess  give  the  following  classification 
of  the  placers  in  Seward  Peninsula: 

(1)  Creek  Placers:     Gravel  deposits  in  the  beds  and  interme- 
diate flood  plains  of  small  streams. 

(2)  Bench  Placers :    Gravel  deposits  in  ancient  stream  channels 
and  flood  plains  which  stand  from  50  to  several  hundred  feet 
above  the  present  streams. 

(3)  Hillside  Placers:     A  group  of  gravel  deposits  intermediate 
between  the  creek  and  bench  placers.     Their  bed  rock  is  slightly 
above  the  creek  bed  and  the  surface  topography  shows  no  sign  of 
benching. 

(4)  River-bar  Placers:     Placers  on  gravel  flats  in  or  adjacent 
to  the  beds  of  large  streams. 

(5)  Gravel-plain  Placers:     Placers  found  in  the  gravels  of  the 
coastal  or  other  lowland  plains. 

(6)  Sea-beach  Placers:     Placers reconcentrated from  the  coastal 
plain  gravels  by  the  waves  along  the  seashore. 

(7)  Ancient   beach   Placers:  Deposits   found   on  the  coastal 
plains  along  a  line  of  elevated  beaches. 

Klondike. — This  important  mining  field  lies  a  little  to  the  east 
of  the  Alaskan  boundary  and  in  the  valley  of  the  Yukon.  The 
auriferous  gravels  of  the  district  occupy  about  one-tenth  the  area 
of  those  in  Seward  Peninsula.  In  fact  the  number  of  miles  of 
creeks  bearing  placer  gold  in  the  Klondike  has  been  catalogued 
as  50  in  comparison  with  750  on  Seward  Peninsula.  The  placers 
of  such  creeks  as  the  Eldorado  and  Bonanza  averaged  richer  than 
any  deposits  on  Seward  Peninsula.  It  was  the  exploitation  of 
these  almost  fabulously  rich  and  relatively  shallow  placers  that 
the  Klondike  gold  output  went  up  with  a  bound,  and  it  is  their 
quick  exhaustion  that  has  caused  so  marked  a  decline  in  their 
annual  yield.  There  are  extensive  deposits  of  lower  grade 
gravels,  but  these  are  not  likely  to  make  the  annual  yield  again 
equal  to  that  of  the  banner  year.  (See  Fig.  60.) 


82 


ECONOMIC  GEOLOGY 


FIG.  60. — Dredges  on  No.  104  below,  on  Bonanza  Creek,  Yukon  Territory, 
Hydraulic  plant  in  operation  on  hill  in  the  distance.  (After  D.  D.  Cairnes, 
Canadian  Geological  Survey.) 


FIG.  61. — The   Dome  mill,    Porcupine   district,    Ontario,    for    cyaniding 
gold.     Showing  inclined  conveyor. 


PRECIOUS  METALS 


83 


Porcupine. — The  porcupine  district  represents  a  new  field.  It 
is  situated  in  the  northern  part  of  Ontario.  The  most  important 
counties  thus  far  exploited  are  Doloro,  Shaw,  Tisdale  and 
Whitney.  In  these  four  counties  practically  all  of  the  ground 
has  been  staked.  The  Dome  mines  represent  the  pioneer  work 
in  this  field.  Within  the  first  100  ft.  from  the  grass  roots  the 
company  is  said  to  have  actually  blocked  out  $8,000,000  of  gold. 
The  field  bids  fair  to  be  a  large  producer. for  three  reasons.  (1) 
Its  own  native  richness;  (2)  the  great  number  of  scattered  free 
gold  discoveries,  and  (3)  the  completion  of  the  railroad  to  Por- 
cupine during  the  summer  of  1911.  The  geology  of  the  district 
is  represented  by  a  series  of  pre-Cambrian  metamorphics  traversed 


FIG.  62. — Structural  arrangement  of  the  Silurian  slates  and  sandstones 
at  Bendigo,  Australia,  in  which  the  auriferous  saddle-reefs  are  found. 
(After  Thomas  and  MacAlister's  Geology  of  Ore  Deposits.} 

by  a  diabase  of  post-middle  Huronian  age.  The  gold  is  free  mil- 
ling and  the  most  important  gangue  is  quartz.  (See  Fig.  61.) 
The  Geological  Horizon  of  Gold:  Gold  may  be  found  in  small 
quantities  in  nearly  all,  if  not  all,  geological  formations.  It  is 
especially  abundant  in  the  pre-Cambrian,  Ordovician,  Cretaceous 
and  Tertiary  formations,  that  is,  in  general,  in  the  older  rocks,  but 
the  last  two  are  among  the  younger  formations.  The  Silurian 
Devonian  and  Carboniferous  terranes  are  not  known  to  carry 
gold  in  paying  quantities  in  the  United  States,  but  in  British 
Columbia  gold  occurs  in  the  Carboniferous  strata.  However  it 
is  possible  that  some  of  the  gold-bearing  rocks  of  the  Appalachian 
belt  are  as  late  as  the  Carboniferous,  but  in  the  main  they  are 
Cambrian  and  Ordovician.  (See  Fig.  62.) 


84 


ECONOMIC  GEOLOGY 


Methods  of  Placer  Mining. — In  the  early  history  of  placer 
mining,  only  a  few  feet  of  earth  next  to  the  bed  rock  and  the  up- 
per surface  of  the  bed  rock  itself  was  panned,  washed  or  sluiced, 
for  the  richest  portion  of  the  entire  placer  lies  near  the  bed  rock. 
The  earliest  method  of  reclaiming  the  gold  was  by  panning.  This 
was  followed  by  the  rocker,  the  long-torn  and  sluice-box,  the 
ground  sluice,  drift  mining,  the  monitor,  the  hydraulic  elevator 
and  the  electric  dredge.  In  the  hydraulic  process,  the  entire 
placer  is  washed  by  carrying  the  auriferous  gravel  into  sluices 
across  which  riffles  are  placed  for  the  extraction  of  the  gold.  In 


FIG.  63.— American  Hill  Placer  mine,  Elk  City,  Idaho.    (After  W.  Lindgren, 
U.  S.  Geological,  Survey.} 

some  cases  mercury  is  placed  upon  the  riffles  and  the  free  gold 
unites  with  the  mercury  in  the  formation  of  an  amalgam.  (See 
Fig.  63.) 

More  than  one-fourth  of  the  gold  mined  in  California  at  present 
is  obtained  through  dredging,  mostly  from  ground  previously 
mined.  The  electric  dredge  has  solved  the  problem  of  mining 
the  gravels  below  the  water  level  and  in  rapidly  flowing  streams 
(Fig.  64). 

The  chief  difficulty  of  placer  mining  in  the  Klondike  is  the 
permanently  frozen  ground,  which  has  led  to  certain  peculiarities  in 


PRECIOUS  METALS 


85 


the  method  adopted.  Every  yard  of  the  gravel  which  is  sluiced 
must  first  be  thawed  either  by  artificial  means  or  by  exposing  it 
to  the  rays  of  the  summer  sun,  after  stripping  off  the  muck  that 
overlies  the  auriferous  gravels.  It  is  impossible  to  work  the  frozen 


FIG.  64. — Hydraulic  mine  at  Cherokee;  Butte  County,  California.     (After 
J.  S.  Diller,  U.  S.  Geological  Survey.) 

ground  with  pick  and  spade,  or  even  with  explosives  to  loosen  the 
gravel. 

Steam  thawing  is  the  most  efficient  method  now  in  use.  Iron 
pipes,  4  to  6  ft.  in  length,  tipped  with  steel  nozzles,  are  inserted 
into  the  gravel  and  then  steam  is  forced  through  them  at  a  pres- 
sure of  about  120  Ib.  per  square  inch.  These  pipes  are  known  as 


86  ECONOMIC  GEOLOGY 

points,  one  point  being  inserted  in  each  square  yard,  and  driven 
gradually  by  a  hammer.  Each  point  will  thaw  from  2  to  5  cu.  yd. 
of  gravel  per  day. 

The  washing  of  the  gravel  is  usually  done  by  sluices.  These  are 
long  wooden  troughs  made  in  12-ft.  lengths,  and  about  10  in.  broad. 
The  bottom  is  lined  with  wooden  riffles  consisting  generally  of 
longitudinal  bars,  by  which  the  gold  and  heavy  minerals  are  caught. 
The  common  sluice  head  has  a  fall  of  8  in.  in  the  12  ft.  and  has 
a  capacity  of  120  cu.  ft.  per  minute. 

Water  is  very  scarce  in  some  districts  and  must  be  used  econom- 
ically. In  some  instances  the  water  is  conducted  for  long  dis- 
tances in  sluice  boxes.  In  case  the  valley  is  wide  and  the  pay 
streak  is  on  the  opposite  side  of  the  valley  from  the  stream,  the  water 
is  raised  by  centrifugal  pumps  to  a  height  of  30  or  40  ft.  and 
conveyed  across  the  valley  by  a  long  flume.  In  the  final  wash-up 
by  which  the  gold  is  recovered  from  the  sluice  boxes  the  riffles  are  re- 
moved and  a  copious  stream  of  water  sent  down  the  sluice  which 
carries  away  the  fine  gravel  and  leaves  the  gold  and  the  heavy 
black  sand  that  accompanies  it.  When  dry,  the  sand  is  removed 
by  blowers. 

The  placer  mining  upon  creeks  and  hillsides  is  somewhat  dif- 
ferent. On  a  creek  a  shaft  is  sunk  down  to  bed  rock.  Four  lat- 
eral drifts  are  driven  from  the  shaft  along  the  surface  of  the  bed  rock, 
and  opened  out  in  a  fan-like  manner,  to  the  limits  of  the  claim. 
The  outermost  portions  are  worked  first,  and  the  ground  is  mined 
toward  the  shaft,  or  retreating.  During  the  retreat  the  rock  and 
the  overlying  muck  are  allowed  to  cave  and  settle  down  to  the  bed 
rock.  Timbering  is  thus  entirely  avoided.  The  frozen  grounds 
require  no  support,  and  chambers  often  100  ft.  square  are  found 
covered  by  an  icy  roof  of  muck. 

Amalgamation. — For  amalgamation,  the  ore  must  be  free  mill- 
ing, that  is,  not  require  roasting  before  the  gold  or  silver  will 
unite  directly  with  mercury.  The  ore  is  first  crushed  to  a  size 
varying  from  1  to  2  in.  in  diameter.  It  then  passes  with 
water  to  the  stamps  where  it  is  reduced  to  an  impalpable  pulp. 
It  is  then  carried  over  plates  covered  with  silver-plated  amalga- 
mated copper.  From  these  plates  it  passes  directly  to  concen- 
trating tables  or  Frue  vanners  where  the  sulphides  are  separated 
by  their  higher  specific  gravity  and  shipped  direct  to  the  smelter. 
The  tailings  comprise  that  portion  that  goes  into  the  streams  as 
waste.  The  plates  were  formerly  made  .of  copper,  but  the  copper 


PRECIOUS  METALS  87 

did  not  catch  all  the  gold.  The  silver-plated  amalgamated  cop- 
per plate,  which  has  taken  its  place,  saves  15  per  cent,  more  gold 
than  the  old  copper  plates,  and  the  gold  caught  above  the 
blankets  is  16.72  per  cent,  greater.  The  old  copper  plates  were  in- 
efficient for  three  reasons:  (1)  They  tarnish  quickly,  and  the 
amalgam  passes  over  the  tarnished  surface.  This  has  to  be  re- 
moved by  washing  the  plates  with  KCN  solution.  (2)  The  amal- 
gam is  loosened  from  the  plates  by  the  washing  with  KCN  and 
mechanically  lost.  (3)  The  chemical  loss  of  amalgam  by  the 
same  agent  through  solution  is  great.  The  total  loss  of  gold 


FIG.  65. — Iron  Crown  quartz  mill,  Newsome   Creek,     Idaho.     (After  W. 
Lindgren,  U.  S.  Geological  Survey.) 

is  frequently  10  per  cent.,  but  by  improved  methods  in  washing 
and  general  treatment  of  the  ore  95  to  98  per  cent,  of  the  total 
gold  content  is  recovered.  (See  Fig.  65.) 

Cyanide  Process. — The  ore  is  crushed  and  treated  with  a  solu- 
tion of  KCN,  when  a  double  cyanide  of  gold  and  potassium  is 
obtained.  The  double  cyanide  is  often  catalogued  KAu(CN)2, 
and  from  this  solution  the  gold  is  precipitated  by  metallic  zinc. 
One-half  pound  of  zinc  is  required  per  ton  of  solution,  the  total 
cost  then  per  ton  for  precipitation  is  12  cents;  and  a  profit  can 
be  obtained  where  only  3  grains  of  gold  exist  in  a  ton  of  solution. 


88  ECONOMIC  GEOLOGY 

The  zinc  may  be  used  in  the  form  of  zinc  dust,  shavings,  granu- 
lated zinc  or  sheet  zinc,  but  the  zinc  dust  is  generally  preferred 
because  it  exposes  a  larger  percentage  of  the  surface  to  the 
action  of  the  solution.  The  following  equation  shows  the  re- 
action that  might  take  place. 

2KAu  (CN)2+Zn  =  K2Zn(CN)4-h2Au. 

The  process  is  applicable  to  certain  free  milling  ores,  to  refrac- 
tory ores,  but  was  designed  especially  for  the  treatment  of  tail- 
ings which  were  allowed  to  flow  to  waste  for  many  years.  Many 
western  plants  now  have  their  cyanide  plant  in  connection  with 
their  amalgamation  plant. 

Chlorination  Process.  —  This  is  not  applicable  to  free  milling 
ores  carrying  nuggets,  but  to  sulphides  carrying  large  quantities 
of  free  gold.  The  ore  is  crushed,  roasted,  weighed  and  then 
charged  into  barrels  with  18  tons  capacity,  6|  ft.  in  diameter  and 
15  ft.  long.  Nascent  chlorine  is  the  solvent.  The  solution  from 
the  barrels  passes  to  a  filter  tank  for  the  removal  of  the  sand. 
From  the  filter  tank  it  passes  to  a  settling  tank  for  the  removal 
of  the  fine  particles  held  in  suspension;  from  the  settling  tank  it 
passes  to  the  precipitation  tank,  in  which  is  placed  zinc  ribbons, 
scrap  zinc,  or  zinc  dust.  Hydrogen  sulphide  is  sometimes 
passed  into  these  tanks,  and  the  resulting  gold  is  reasonably  pure, 
but  charcoal  is  the  most  efficient  reducing  agent,  and  the  gold  ob- 
tained is  0.995  fine, 


Reduction  by  Sodium  Thiosulphate.  —  A  solution  of  Na2S203 
for  the  extraction  of  gold  and  silver  has  far  greater  solvent  power 
than  potassium  cyanide  and  is  non-toxic  in  its  physiological  effect. 
It  can  be  prepared  in  large  quantities  at  low  price  according  to 
the  following  formula: 

2  parts.  Na2S203;  2  parts.  CH3C02Na;  3/4  part.  FeCl3;  add  10 
times  the  volume  of  H20.  This  will  dissolve  from  15  to  20  times 
as  much  gold  in  10  hours  as  a  2  per  cent,  solution  of  potassium 
cyanide,  2  per  cent,  being  the  maximum  strength  allowable  in 
cyanide  solutions.  The  gold  can  be  recovered  from  the  solution 
by  zinc  shavings,  zinc  dust,  zinc  ribbons,  and  by  electrolysis. 
The  cost  of  treatment  by  this  process  is  estimated  at  $2.75  per  ton. 

Reduction  by  Electrolysis.  —  Gold  is  readily  separated  by  elec- 
trolysis from  its  various  solutions,  and  in  this  method  of  treat- 


PRECIOUS  METALS  89 

ment,  silver-plated  amalgamated  copper  plates  are  not  as 
effective  as  the  older  type.  Copper,  iron  and  lead  plates  are 
used  in  the  order  of  their  efficiency.  Copper  is  more  effective 
than  iron  and  iron  is  more  effective  than  lead.  The  silver-plated 
amalgamated  copper  plates  are  profitable  only  when  a  current 
of  low  density  is  employed. 

Uses  of  Gold. — Gold  is  used  in  the  various  arts  and  industries, 
for  coinage;  for  jewlery,  spectacles,  and  pen  making;  in  den- 
tistry, and  in  chemical  and  photographic  work.  The  beaten  gold 
leaf  is  used  for  gilded  letters  of  signs,  for  lettering  on  book  bind- 
ings, for  book  edges,  for  mirror  frames  and  picture  frames,  for 
gilding  metals.  Gold  dust  is  used  in  the  moulding  of  furniture 
or  room  decoration.  The  Japanese  use  gold  largely  in  the  manu- 
facture of  lacquers.  Gold  is  drawn  into  wire  and  used  for  gold 
lace,  and  other  decorations. 

It  may  be  of  interest  to  know  the  relative  proportion  that 
enters  into  these  different  fields:  For  coinage,  44  per  cent.;  for 
jewlery,  24  per  cent.;  for  exportation,  10  per  cent.;  watch  cases, 
10  per  cent.;  gold  leaf,  2  1/2  per  cent.;  watch  chains,  1  3/4  per 
cent.;  pens,  dentistry  and  mechanical  work,  11/4  per  cent.;  for 
gold  plate,  3/4  per  cent.  All  these  uses  may  be  catalogued  as  its 
use  in  American  arts  and  industries.  This  will  give  for  indust- 
ries 40  per  cent.,  coinage  44  per  cent.;  exportation  10  per  cent. 
These  are  based  directly  upon  the  coining  value  of  the  metal,  or 
$20.67  per  Troy  ounce. 

SILVER:  ITS  PROPERTIES,  SOURCE  AND  USES 

Properties. — Silver,  symbol  Ag,  is  known  as  the  white  metal. 
It  is  pure  white  and  susceptible  of  very  high  polish.  When  it  is 
in  the  form  of  a  powder,  it  has  a  gray  or  earthy  appearance.  It 
is  malleable,  ductile,  and  sectile,  so  that  it  can  be  rolled  or  ham- 
mered into  thin  sheets  and  readily  drawn  out  into  extremely  fine 
wire.  It  is  the  best  conductor  of  electricity  known  and  its  con- 
ductivity is  increased  by  the  process  of  annealing.  It  is  harder 
than  gold,  and  softer  than  copper.  It  is,  therefore;  alloyed  with 
copper  in  coinage.  For  United  States  coinage  the  standard  is 
nine  parts  of  silver  to  one  part  of  copper.  Its  specific  gravity 
is  10.50  when  cast,  and  10.57  when  struck  by  the  die  in  coinage. 
Its  melting  point  is  955°  C.,  and  its  atomic  weight  is  107.88. 

Ores  of  the  Metal. — Silver  occurs  native  containing  small 
quantities  of  gold,  copper,  iron,  cobalt  and  antimony.  It  occurs 


90  ECONOMIC  GEOLOGY 

as  threads  or  plates  through  the  reduction  of  other  ores  of  silver, 
or  it  may  occur  deposited  as  a  film  over  other  minerals  or  rocks, 
as  copper  or  carboniferous  shale.  The  other  ores  of  silver  are  as 
follows : 

Argentite,  Ag2S,  containing  87.1  per  cent,  silver,  the  only  black 
and  sectile  sulphide  of  silver,  the  most  unstable  of  all  the  sul- 
phides of  the  commoner  metals;  pyrargyrite,  3Ag2S,Sb2S3,  con- 
taining 59.9  per  cent,  silver;  stephanite,  5Ag2S,Sb2Ss,  containing 
68.5  per  cent,  silver;  polybasite,  9Ag2S,Sb2S3,  containing  75.6 
per  cent,  silver;  proustite,  3Ag2S,As2Ss,  containing  65.4  per  cent, 
silver. 

Silver  occurs  also  in  association  with  copper  minerals ;  as  tetra- 
hedrite,  4Cu2S,Sb2S3;  although  no  silver  is  present  in  the  for- 
mula, samples  of  this  ore  have  given  500  Ib.  of  silver  to  the  ton; 
tennantite,  4Cu2S,As2S3,  sometimes  bears  silver. 

Silver  occurs  abundantly  in  argentiferous  galenite.  All  gale- 
nite  is  more  or  less  argentiferous,  but  the  finely  crystalline  variety 
contains  more  silver  than  the  coarse  mineral.  Silver  occurs  with 
tellurium  in  hessite,  Ag2Te,  containing  63.3  per  cent,  of  silver;  in 
petzite,  displacing  gold,  for  petzite  is  a  telluride  of  gold  (Ag,Au)r 
Te.  It  occurs  in  combination  with  selenium  in  naumanite,  PbSe,- 
13Ag2Se.  and  also  as  the  selenide  alone,  Ag2Se.  It  occurs  with 
bismuth,  copper  and  mercury,  but  perhaps  more  important  as  the 
amalgam.  This  implies  varying  combinations  of  silver  and  mer- 
cury. Instead  of  the  direct  union  in  the  line  of  atomic  weights, 
seems  to  unite  with  mercury  in  almost  all  proportions.  The 
amalgam  contains  27.5  per  cent,  to  95.8  per  cent,  of  silver. 

Silver  occurs  again  in  combination  with  the  halogens.  The 
most  important  haloids  of  silver  are:  Cerargyrite,  AgCl,  with  75.3 
per  cent,  of  silver;  embolite,  3AgCl,AgBr,  containing  66.9  per 
cent,  silver;  bromyrite,  AgBr,  containing  57.4  per  cent,  of  silver; 
iodyrite,  Agl,  containing  45.2  per  cent,  silver.  All  of  these  haloid 
minerals  are  soft  and  sectile. 

Silver  is  very  widely  distributed  in  nature.  It  is  produced  by 
practically  all  countries  of  the  world,  although  many  of  them  pro- 
duce only  a  small  quanity  of  the  metal.  It  has  been  observed  as 
a  natural  constituent  of  igneous  rocks.  It  has  been  detected  in 
common  salt,  in  sea  weed,  in  sea  water,  and  in  corals.  In  most 
cases  native  silver  is  of  secondary  origin,  the  metal  being  derived 
from  the  reduction  of  the  sulphides  and  antimonides  of  silver. 
Organic  matter  is  a  common  reducing  agent  effecting  the  precipi- 


PRECIOUS  METALS  91 

tation  of  silver  in  a  metallic  state.  Pyrite,  chalcopyrite,  and 
many  other  sulphides,  reduce  silver  solutions  readily  to  the 
metallic  state.  According  to  Dr.  F.  W.  Clarke,  the  metal  will  be 
precipitated  by  any  reaction  in  which  nascent  hydrogen  is 
brought  in  contact  with  a  silver  solution.  The  nature  of  silver 
solutions  in  metalliferous  veins  is  not  positively  known.  Silver 
sulphate  is  readily  formed  by  the  oxidation  of  the  sulphide, 
and  that  will  be  transformed  into  the  chloride  by  percolating 
chlorine-bearing  waters.  The  antimonides,  arsenides,  and  selen- 
ides  of  silver  are  rarer  minerals,  and  are  of  only  small  impor- 
tance in  the  production  of  the  metal.  These  by  subsequent 
enrichment  might  become  of  commercial  importance. 

Character  of  Ore  Bodies. — At  Butte,  Montana,  the  ore  occurs 
as  native  silver,  with  galenite  in  veins  of  quartz-bearing  manganese. 
These  are  true  fissure  veins  cutting  irruptive  granite.  At  Granite 
Mountain,  20  miles  from  Butte,  the  ore  is  ruby  silver  associated 
with  gold  in  a  true  fissure  vein  cutting  a  gray  granite.  At  Neihart, 
the  ore  occurs  in  veins  in  gneiss  and  other  igneous  rocks,  mostly 
as  replacement  deposits  which  have  been  subsequently  fractured 
and  secondarily  enriched.  Argentiferous  galenite  is  common  in 
Montana  as  contact  deposits  between  porphyritic  igneous  rocks 
and  Carboniferous  limestone. 

In  the  production  of  silver,  Colorado  ranks  high,  the  chief  sil- 
ver-producing region  of  the  state  being  Leadville.  This  district 
is  situated  in  the  Mosquito  Range  near  the  headwaters  of  the 
Arkansas  river.  It  began  its  history  in  1860  as  a  gold  camp, 
but  upon  exhaustion  of  the  gold  resources  the  camp  lost  -its 
significance  as  such.  It  then  became  a  silver-producing  camp 
which  position  it  lost  nearly  a  decade  ago  when  Leadville  became 
a  lead  and  zinc  camp.  Eight  or  ten  different  metals  are  produced 
within  the  camp  at  the  present  time. 

The  Geology  of  Leadville. — The  base  of  the  mountain  consists  of 
a  series  of  Archean  granites,  gneisses,  schists  and  amphibolites. 
These  are  overlain  by  a  series  of  Cambrian  quartzities  and  shales 
which  in  turn  are  covered  by  Silurian  limestones  and  quartzites. 
Above  these  there  appear  limestones,  shales  and  grits  of  Carbon- 
iferous age.  Associated  with  this  vast  series  of  sedimentaries 
there  appears  also  many  late  Mesozoic  and  Tertiary  irruptives 
(Fig.  66.) 

The  uplift  of  the  Mosquito  Range,  of  which  the  Leadville  dis- 
trict forms  the  western  slope,  resulted  in  a  series  of  anticlinal  and 


92  ECONOMIC  GEOLOGY 

synclinal  folds  with  many  faults  that  have  the  same  general 
direction  as  the  axes  of  the  fold.  They  do  not  coincide  exactly 
with  them  but  pass  into  folds  at  their  extremities.  The  folds  are 
nearly  vertical  on  their  western  slope  and  less  inclined  on  the  east. 
It  is  along  the  higher  and  steeper  slope  that  the  greatest  amount 
of  fracturing  has  taken  place.  (Fig.  67.) 

Faults:     The  displacement  in  general  has  been  toward  the 
east.     The  maximum  upthrow  in  any  one  fault  is  recorded  in  the 


FIG.  66. — View  from  the  top  of  Carbonate  Hill,  Leadville,  Colorado, 
looking  toward  Iron  Hill.  The  valley  in  center  ground  marks  position  of 
the  Iron  fault.  Shaft  house  is  that  of  the  Tucson  shaft,  and  ridge  in  distance 
fault  scarp  of  Mosquito  Range.  (By  permission  of  the  Macmillan  Company, 
from  Ries1  Economic  Geology.) 

Mosquito  fault,  measuring  about  5000  ft.  The  mineral  veins 
themselves  have  been  folded  and  faulted  with  the  enclosing 
sedimentary  and  eruptive  rocks.  This  fact  alone  would  prove 
that  the  mineral  deposition  took  place  prior  to  the  dynamic 
movements  that  formed  the  Mosquito  Range  itself.  (See  Fig. 
68.) 

Mode  of  Occurrence:  The  typical  form  of  the  Leadville  de- 
posits seem  to  be  a  contact  sheet  whose  upper  surface  is  the  Lead- 


PRECIOUS  METALS 


93 


FIG.  67. — View  from  south  end  of  Carbonate  Hill,  Leadville,  Colorado, 
overlooking  California  Gulch  in  foreground  and  town  of  Leadville  in  the 
valley,  Sawatch  Range  in  distance.  (By  permission  of  the  Macmillan  Com- 
pany, from  Ries'  Economic  Geology.) 


Gray  Porphyry 
White  Limestone 
Blue  Limestone 
l'-Vv-v-'J  Oraand  Vein  Material 
Lower  Quartzi 


FIG.  68. — East-west  section  through  the  McKeon  shaft,  Leadville,  Colorado, 
showing  the  faulted  ore  bodies  along  the  contacts.     (After  Blow.) 


94  ECONOMIC  GEOLOGY 

ville  porphyry  with  a  regular  and  well-defined  upper  limit  to  the 
ore  body.  The  ore  occurs  in  the  blue  limestone  of  Carboniferous 
age.  The  lower  surface  of  the  ore  body  is  irregular  and  often  ill 
defined.  It  sometimes  occupies  the  entire  thickness  of  the  lime- 
stone formation.  The  ore  sometimes  occurs  near  the  contact  of 
the  gray  porphyries  with  the  blue  limestone,  sometimes  in  both 
the  calcareous  and  siliceous  beds,  sometimes  in  the  porphyries 
themselves  either  near  contact  surfaces  or  along  joint  and  fault 
planes.  As  a  rule  the  argentiferous  lead  ores  occur  in  the  blue 
magnesian  limestone  while  the  auriferous  pyrites  and  the  copper 
ores  are  more  frequently  found  in  the  quart zites  and  porphyries. 

Leadville  Minerals :  Native  gold  in  flakes  or  leaflets;  the  silver 
minerals  are  argentiferous  galenite,  cerargyrite,  embolite  and 
native  silver;  the  lead  minerals  are  galenite,  cerussite,  anglesite, 
massicot  minium,  and  wulfenite;  the  accessory  minerals  are 
sphalerite,  calamine,  stibnite  realgar,  bismuthinite,  malachite, 
chrysocolla,  wulfenite,  a  vanadate  of  lead  and  zinc,  pyrite,  and 
hydrous  and  anhydrous  oxides  of  iron.  The  gangue  minerals 
are  quartz,  pyrite,  siderite,  barite,  gypsum  and  hydrous  silicates 
of  aluminum. 

Origion  of  the  Ores:  According  to  S.  F.  Emmons,  the  ores 
were  derived  from  a  descending  aqueous  solution.  The  ores  de- 
rived their  metallic  content  from  the  neighboring  eruptive  rocks. 
Mr.  Emmons  further  contends  that  the  metals  must  have  been 
formed  beneath  a  thickness  of  at  least  10,000  ft.  of  superincum- 
bent rocks  and  an  unknown  amount  of  sea  water;  that  if  they  had 
been  deposited  from  hot  ascending  solutions  as  the  result  of  the 
relief  of  pressure  it  would  naturally  be  expected  that  the  bulk 
of  the  deposit  would  have  been  found  in  the  upper  part  of  this 
mass  of  rocks  where  the  pressure  was  the  least,  rather  than  at  the 
base;  that  at  the  time  of  deposition  the  sedimentary  beds  were 
horizontal  and  relatively  undisturbed;  that  if  the  deposits  had 
been  made  from  ascending  currents  the  process  of  deposition 
would  have  acted  from  the  bottom  upward  instead  of  from  the 
upper  surface  downward  as  is  shown  in  the  case  of  the  blue 
limestone  which  carries  the  bulk  of  the  ores;  that  in  the  region  of 
the  greatest  ore  development  there  is  a  noticable  absence  of 
channels  extending  downward  through  which  ascending  solu- 
tions might  have  come;  that  the  vast  majority  of  irruptive  bodies 
are  in  the  form  of  horizontal  sheets  parallel  with  the  stratifica- 
tion; and  that  the  few  approximately  vertical  bodies  afford  no 


PRECIOUS  METALS  95 

evidence  that  their  walls  form  part  of  a  channel  through  which 
the  ore  currents  came  up  from  below. 

Since  the  work  of  Mr.  Emmons  was  done  at  Leadville,  other 
eminent  geologists  have  been  in  the  field  with  better  opportunity 
to  study  the  origin  of  the  ore  deposits.  The  finding  of  fissure 
ores  in  the  Cambrian  quartzite  leads  them  to  the  conclusion 
that  the  ores  may  have  been  brought  in  by  solutions  ascending 
directly  from  the  intrusives. 

In  1859,  placer  gold  was  found  in  California  Gulch,  worked  out 
in  1863  and  deserted.  The  owners  were  much  troubled  with 
heavy  rock,  the  composition  of  which  was  unknown  to  the  miners, 
but  later  discovered  to  be  cerussite,  the  carbonate  of  lead,  rich 
in  its  silver  content. 

In  1875  these  deposits  were  reopened  and  worked  for  their 
silver  content.  The  silver  occurs  as  argentite,  native  silver, 
cerargyrite  and  embolite  at  the  surface  and  in  galenite  at  greater 
depths.  Masses  of  auriferous  galenite  have  been  found  100  ft. 
in  thickness. 

At  Aspen,  oxidized  lead  and  silver  ores  occur  in  highly  folded 
and  faulted  Carboniferous  limestone.  According  to  W.  H.  Weed, 
the  accumulation  of  ore  at  the  intersection  of  fault  planes  is  the 
result  of  a  secondary  enrichment  rather  than  of  primary  concen- 
tration. At  Creede,  the  silver  ores  occur  in  fissure  veins  pene- 
trating igneous  rocks.  At  Red  Mountain  the  silver  ores  occur 
in  true  fissure  veins  traversing  Jura-Trias  terranes. 

Utah. — Third  in  order  of  importance  as  a  silver  producer  is 
Utah.  In  both  Cottonwood  canons,  oxidized  lead-silver  ores 
occur  near  the  surface  in  bedded  veins  in  Carboniferous  lime- 
stone. In  Beaver  County  oxidized  lead  and  silver  ores  occur  in 
contact  fissures  in  the  Horn  Silver  mine;  in  " chamber  deposits" 
in  Carboniferous  limestone  at  the  Cave  mine;  in  fissures  at  the 
Carbonate  mine;  in  Park  City,  as  silver  and  lead  oies  in 
Carboniferous  limestone,  sandstone;  and  shales.  The  ores 
bearing  lead  and  copper  are  oxidized,  the  others  appear  mostly 
as  bedded  deposits  in  the  limestone,  often  with  siliceous  walls 
separating  one  deposit  from  another.  These  are  frequently 
associated  with  porphyritic  igneous  rocks.  In  Idaho  at  Coeur 
d'  Alene  the  ore  galenite  is  found  with  siderite  gangue  in  highly 
folded  quartzites  and  mica  schist. 

Nevada — The  Comstock  lode,  Nevada,  represents  the  largest 
auriferous  silver- bearing  deposit  ever  discovered.  It  lies  in  a 


96  ECONOMIC  GEOLOGY 

great  fissure  vein  several  hundred  feet  in  width  and  four  miles 
long  with  branching  ends.  The  fissure  follows  a  fault  line,  and 
at  the  center  where  the  displacement  is  the  greatest  the  width  is 
300  ft.  The  mine  reaches  a  depth  of  nearly  one  mile.  All  the 
veins  were  originally  opened  for  silver,  for  they  contain  silver  at 
the  surface.  As  the  veins  were  worked  to  lower  depths  copper 
ores  appeared.  The  silver  soon  became  refractory  and  the  per- 
centage too  small  for  profitable  extraction. 

The  ore  occurs  in  true  fissure  veins  bearing  native  silver 
and  the  silver  sulphides,  associated  with  zinc  and  manganese. 
The  gangue  consists  of  rhodonite,  rhodochrosite,  and  quartz. 
Probably  there  were  no  open  fissures  before  the  deposit  occurred 
for  the  ore  is  deposited  along  fractures  or  cracks  impregnating  and 
partially  replacing  the  wall  rock,  so  that  there  is  a  gradual  joining 
of  the  vein  and  the  wall  rock  with  no  sharp  line  of  demarcation 
between  them. 

The  surface  ore  is  black  due  to  such  manganese  compounds  as 
pyrolusite,  MnO2,  resulting  from  the  breaking  down  of  manganese 
minerals.  At  the  lower  depths  the  mineral  remains  pink,  the 
natural  color  of  rhodonite  and  rhodochrosite.  A  conical  peak 
2000  ft.  above  the  valley  is  cut  by  a  pure  white  vein  of  quartz 
containing  ruby  silver  in  little  red  specks  with  traces  of  pyrite, 
galenite  and  sphalerite.  This  locality  is  remarkable  for  the  depth 
of  the  oxidation  of  the  ore  reaching  1400  ft.  on  the  sides  and  1000 
ft.  in  the  center  of  the  mound.  This  was  a  very  important  field 
in  the  production  of  silver  before  the  decline  in  the  price  of  the 
metal.  The  country  rock  is  basic,  diabase  and  diorite. 

In  the  Eureka  district,  oxidized  lead  and  silver  ores,  auriferous 
to  a  considerable  degree,  occur  in  a  brecciated  Cambrian  lime- 
stone and  shale. 

New  Mexico. — In  the  Lake  Valley  district  there  occur  galenite, 
cerussite  and  embolite  in  Paleozoic  limestone.  At  Silver  City  in 
the  Breman  mine,  argentite  and  cerargyrite  occur  at  the  contact 
of  shale  and  limestone  impregnating  both.  At  Lone  Mountain 
cerargyrite,  bromyrite  and  embolite  occur  in  a  gangue  of  quartz. 

In  Wardner  County  and  Bitter  Root  Mountain,  Idaho,  galenite 
occurs  in  quartzite  and  mica  schist  in  large  chutes  impregnating 
the  fissured  hanging  walls.  This  is  one  of  the  most  productive 
regions  of  the  world. 

In  the  Thames  district  the  gold-silver  lodes  consist  mainly  of 
quartz,  in  which  both  metals  are  present  in  threads,  foils  and 


PRECIOUS  METALS  97 

grains.  The  district  is  cut  through  by  two  Pliocene  faults,  and 
the  ores  are  associated  with  Tertiary  eruptives.  The  ores  are  of 
hydatogenetic  origin. 

In  the  Freiberg  district  the  lodes  occur  in  metamorphic  acidic 
intrusives.  The  ores  are  native  silver,  argentite  and  proustite. 
The  silver  ores  of  Japan  belong  to  the  acidic  type  associated  with 
Tertiary  eruptives. 

Ontario,  Canada. — In  the  Province  of  Ontario  there  are  three 
important  silver  districts.  In  the  order  of  their  discovery  they 
are  Cobalt,  South  Lorrain  and  Gowganda.  The  rocks  are  essen- 
tially alike  in  the  three  fields.  The  sedimentaries  consist  of 
conglomerates,  slates  and  schists  of  pre-Canbrian  age.  The 
intrusives  are  diabases,  gabbros  and  granites.  The  silver  lodes 
traverse  the  irruptives  and  often  the  veins  penetrate  the  sedimen- 
taries. The  veins  vary  in  width  from  a  fraction  of  an  inch  to  two 
feet  or  more.  The  ores  are  of  hydrothermal  origin.  The  silver 
minerals  are  native  silver,  argentite,  pyrargyrite,  and  breithaup- 
tite,  associated  with  smaltite,  niccolite,  pyrite,  chalcopyrite, 
erythrite  and  annabergite.  The  principal  gangue  mineral  is 
calcite.  Quartz  is  sometimes  present  in  subordinate  quantity. 
There  seems  to  have  been  a  distinct  order  of  deposition  of  miner- 
als in  the  Cobalt  district.  According  to  Prof.  Wm.  Campell 
of  Columbia  University,  smaltite  was  first  introduced  into  fissures 
in  the  diabase,  etc.  This  introduction  was  followed  by  niccolite 
and  small  quantities  of  other  ores.  Then  there  came  a  period 
of  disturbance  in  which  the  vein  materials  were  brecciated. 
The  infiltration  of  calcite  and  the  deposition  of  native  silver 
in  plates  and  threads  and  grains  followed  later.  Finally  bis- 
muth ores  were  introduced  into  a  few  veins.  The  author  has 
worked  out  the  same  order  for  several  mines  in  the  Gowganda 
district. 

Geographical  Distribution  of  the  Ore. — Silver  occurs  in  all 
countries.  It  is  most  abundant  in  Mexico,  United  States,  Canada, 
Australia  and  Germany,  arranged  in  order  of  importance.  In 
the  United  States  the  distribution  of  silver  is  in  five  distinct 
belts:  (1)  The  Appalachian;  (2)  the  Lake  Superior  district; 
(3)  the  Cordilleran;  (4)  the  Pacific  Coast  belt;  and  (5)  Alaska. 
However,  90  per  cent,  of  all  the  silver  produced  in  the  United 
States  comes  from  Montana,  Colorado,  Idaho,  Utah  and  Nevada. 
Therefore,  the  area  of  greatest  importance  is  the  Cordilleran 
section. 
7 


98  ECONOMIC  GEOLOGY 

Geological  Horizon. — Silver  ores  occur  in  the  rocks  of  all  ages. 
It  is  not  restricted,  therefore,  to  any  one  horizon.  However,  it 
is  especially  abundant  in  the  pre-Cambrian,  Cambrian,  and  Car- 
boniferous rocks.  It  occurs  in  Colorado  in  Jura-Trias  rocks. 
The  character  of  the  deposits  may  be  classified  as  follows:  (1) 
Most  of  the  silver  veins  are  true  fissure  veins;  (2)  the  silver 
occurs  as  bedded  deposits  in  limestone;  and  (3)  as  contact 
deposits  between  igneous  and  sedimentary  rocks. 

Extraction  of  the  Metal. — There  are  five  well-known  processes 
used  in  the  extraction  of  the  white  metal  from  its  various  ores; 
(1)  Amalgamation;  (2)  smelting;  (3)  lixiviation;  (4)  cyanida- 
tion  process;  and  (5)  the  electrolytic  process. 

The  Amalgamation  Process. — This  is  applicable  to  native  silver, 
embolite,  cerargyrite,  bromyrite,  iodyrite.  These  crushed  to  a 
powder,  and  ground  directly  with  mercury  without  any  special 
preparation  readily  form  a  silver  amalgam.  The  haeloids  are 
decomposed  with  a  formation  of  silver  amalgam  and  haloid 
compounds  of  mercury.  In  the  case  of  the  sulphide,  argentite, 
metallic  silver  is  set  free  and  a  sulphide  of  mercury  is  formed,  but 
the  process  is  far  slower  than  in  the  case  of  native  silver  or  the 
halogens.  In  the  case  of  the  arsenides  and  antimonides,  the 
process  is  so  slow  that  it  seems  advisable  to  roast  the  ore  with 
common  salt  prior  to  amalgamation. 

Some  form  of  the  amalgamation  process  has  been  known  for  a 
long  time.  The  arrastra  was  introduced  into  America  in  1557. 
It  was  used  for  a  long  period  of  time  in  Mexico.  The  pro- 
cess is  simple.  The  ore  is  finely  crushed,  treated  with  water, 
placed  in  iron  pans  where  by  revolving  machinery  it  is  ground  to 
an-  impalpable  powder,  and  mixed  with  mercury.  The  revolving 
machinery  is  kept  in  motion  four  to  six  hours,  when  the  mixture 
is  complete.  The  amalgam  is  then  collected  and  mercury  dis- 
tilled at  a  temperature  of  350°,  and  the  silver  fashioned  into 
bullion. 

The  "cazo"  or  " caldron"  process  is  a  simple  method  for  treat- 
ing surface  ores  containing  silver,  either  native  or  in  the  form  of 
chlorides  or  bromides.  The  ore  is  first  crushed,  and  then  finely 
ground  in  the  arrastras  and  charged  into  amalgamating  vessels 
with  salt  and  mercury.  The  small  receptacles  originally  em- 
ployed consisted  entirely  of  copper.  The  fondon  took  its  place. 
This  is  a  larger  receptacle  with  wooden  sides  and  copper  bottom. 
In  the  fondon,  two  copper  blocks  are  fastened  to  arms  attached 


PRECIOUS  METALS  99 

to  the  vertical  revolving  shaft  and  dragged  around  on  the  copper 
bottom  by  motive  power.  It  was  the  tendency  of  the  amalgam 
in  this  process  to  adhere  to  the  copper  plates'  which  first  gave  the 
idea  of  the  introduction  of  silver  plated  amalgamated  copper 
plates  in  the  gold  milling  industry. 

Perhaps  the  pan  amalgamation  process  is  the  direct  outcome  of 
the  cazo  and  fondon  processes  with  the  improved  machinery  as 
introduced  by  Frazer  and  Chalmers  of  Chicago.  The  process  is 
continuous,  and  the  ore  is  roasted  before  the  effective  amalgama- 
tion takes  place,  that  is,  amalgamation  takes  place  far  more 
readily  and  completely  in  the  presence  of  roasted  ore. 

Smelting  Process. — This  refers  to  that  method  of  treatment 
carried  out  largely  in  North  America  and  in  Germany,  where  the 
object  is  to  obtain  a  solution  of  silver  in  lead.  The  smelting  is 
carried  on  in  the  blast  furnace  of  moderate  size  with  a  mixture  of 
ore,  fuel,  and  fluxing  material.  The  smelting  of  silver  ore  with 
lead  is  most  satisfactory  under  the  following  conditions:  (1) 
Where  there  is  an  abundance  of  bituminous  coal  or  natural  gas 
to  serve  as  a  supply  of  fuel;  (2)  where  limestone,  low  in  magne- 
sium, is  available ;  and  (3)  where  large  quantities  of  silver-bearing 
galenite  abound.  The  process  is  not  applicable  to  cupriferous  ores 
and  ores  free  from  lead  or  poor  in  silver.  The  process  admits  of 
a  continuous  discharge  of  lead  through  a  siphon  into  some  bowl  or 
vat,  while  the  slag  is  run  continuously  into  iron  kettles  mounted 
on  tracks  so  that  the  cone-shaped  slags  may  be  easily  transported 
to  the  waste  yards.  Later  the  slags  are  run  into  troughs  in  which 
there  flows  a  strong  current  of  water.  As  the  slag  strikes  the 
water  it  is  immediately  granulated.  It  is  used  for  certain  indus- 
tries, as  in  the  manufacture  of  cement.  The  lead  can  be  ladled 
from  the  bowl,  or  tapped  from  it,  or  allowed  to  run  continuously. 

The  Pattinson  process  depends  upon  the  fact  that  the  alloy  of 
silver  and  lead  can  be  fused  easily  and  the  silver  crystallized 
from  the  lead.  Silver  does  not  form  an  alloy  with  lead  to 
any  considerable  extent  as  the  solution  cools.  Silver  dissolves 
rapidly  in  lead  at  the  temperature  of  fusion  of  the  white  metal. 
In  the  Pattinson  process,  when  the  metal  is  molten  and  allowed  to 
cool  the  lead  is  ladled  out  of  a  large  iron  pot  into  kettles  upon  one 
side  growing  richer  and  richer  in  silver,  and  upon  the  other  side 
poorer  and  poorer  in  silver.  The  material  first  to  crystalize 
would  be  pure  lead.  The  material  last  to  solidify  is  the  silver, 
and  between  the  two,  varying  amounts  of  silver  and  lead  are 


100  ECONOMIC  GEOLOGY 

present.  This  material  is  all  remelted  and  recrystallized. 
This  process  is  continued  until  only  about  0.002  per  cent,  of 
silver  remains  in  the  lead. 

The  Rosan  process  is  largely  like  the  Pattinson  only  the  liquid 
alloy  is  drawn  off  leaving  the  solidified  portion.  The  process  is 
less  delicate  or  efficient  than  the  Pattinson,  giving  0.003  per  cent, 
of  silver  waste  in  the  lead. 

The  Parke's  process  depends  upon  the  formation  of  compounds 
of  zinc  and  silver  when  these  metals  are  melted  together.  The 
alloy  of  zinc  and  silver  is  formed  containing  about  12  per  cent,  of 
silver.  The  zinc  is  added  in  small  amounts  at  different  times. 
In  the  first  solidification  practically  all  the  gold  and  copper  so- 
lidify with  the  zinc.  Upon  the  addition  of  more  zinc  the  silver 
unites  directly  with  the  zinc  in  the  formation  of  the  alloy  AgZni2. 
The  efficiency  of  this  method  is  proven  by  the  amount. of  silver 
remaining  in  the  lead  which  is  about  0.005  per  cent.  The 
final  step  in  the  treatment  of  the  alloys  thus  obtained  is  cupel- 
lation,  in  which  process  the  lead  is  volatilized,  and  the  gold  or 
silver  remains  in  the  cupel. 

Lixiviation  Process. — The  silver  is  dissolved,  and  after  filtering, 
is  precipitated  from  the  clear  liquid  into  metallic  form  by  some 
reagent.  The  process  is  as  follows: 

In  the  treatment  of  argentiferous  copper  matter  the  Ziervogel 
process  has  been  largely  utilized,  in  which  copper,  iron  and  silver 
are  present  and  converted  into  their  sulphates,  then  into  their 
oxides.  The  iron  is  the  first  to  oxidize,  copper  second,  silver 
third.  Just  as  the  silver  begins  to  oxidize  it  is  treated  with 
water,  and  the  silver  is  precipitated  by  scrap  copper.  The  copper 
still  in  solution  is  recovered  by  the  more  electro-positive  metal, 
scrap  iron.  The  process  is  complete  when  the  solution  yields 
with  ammonium  hydroxide  only  a  faint  blue  coloration,  and  when 
no  dense  white  curdy  precipitate  is  obtained  upon  the  addition  of 
common  salt. 

In  the  treatment  of  the  ores  containing  copper  and  iron,  so- 
dium chloride  was  first  used  for  the  conversion  of  the  silver  into 
silver  chloride.  This  process  is  known  as  the  Augustine  proc- 
ess. This,  because  of  its  general  inefficiency,  was  supplanted  by 
the  sodium  thiosulphate,  otherwise  known  as  the  Patera  process. 
This  process  is  more  efficacious,  because  of  its  greater  solvent 
power,  especially  upon  the  arsenates,  and  antimonates  of  silver 
which  are  practically  insoluble  in  the  presence  of  the  sodium 


PRECIOUS  METALS  101 


chloride.  The  sodium  thiosulphate  meihp$  Ji^s,  given  w,ayj  very 
largely  to  the  calcium  thiosulphate  method',  'winch  is  pra'cbically 
identical  in  apparatus  and  method  of  trsafmen^/^-V^y/ith  (Cal- 
cium in  place  of  sodium  as  a  solvent.  The  latter  "process  is  known 
as  the  Kiss  process  from  its  inventor.  But  all  these  in  which 
calcium  thiosulphate  enters  as  a  solvent  are  now  replaced  by  the 
cyanide  process. 

Cyanide  Process.  —  This  method  of  treatment  is  based  upon  the 
fact  that  when  silver  sulphides,  arsenides  and  antimonides,  are 
treated  with  a  solution  of  potassium  cyanide  or  sodium  cyanide, 
a  double  cyanide  of  silver  and  potassium,  or  silver  and  sodium 
is  formed.  The  solution  is  far  more  concentrated  than  in  the 


H 


FIG.  69. — Nevada   Hills   mill,    Fairview,    Nevada,    for   cyaniding   silver. 

case  of  the  treatment  of  gold-bearing  ores  with  potassium  cyanide, 
because  the  silver  minerals  are  less  soluble  in  a  cyanide  solution 
than  the  gold  ores.  The  solution  is  filtered  to  remove  all  sedi- 
ment, and  allowed  to  settle  to  a  perfectly  transparent  liquor. 
It  is  then  drawn  off  into  precipitating  tanks,  and  the  metal 
reduced  to  the  elemental  state  by  granulated  zinc,  zinc  shavings, 
zinc  dust,  as  in  the  treatment  of  gold.  (See  Fig.  69.) 

Electrolytic  Process. — Silver  is  separated  from  argentiferous 
copper  ores  electrolytically  by  sulphuric  acid  and  copper  sulphate. 
The  copper  and  iron  are  dissolved  at  the  anode,  while  gold,  silver 
and  platinum  are  precipitated  at  the  cathode.  In  the  modifica- 
tion of  this  process,  known  as  the  Moebius  process,  large  amounts 


102  ECONOMIC  GEOLOGY 

of  silver  are  now  ;re£;ne,d  in  the  United  States.  The  bath  con- 
sists of  a  solution  of  nitric  acid,  silver  nitrate  and  copper  citrate. 
The.  silver  anoV  copper  are  both  dissolved  at  the  anode.  The 
copper  remains  in  solution,  the  silver  is  precipitated  at  the 
cathode,  the  gold  remains  undissolved. 

Uses  of  Silver. — Silver  was  used  by  the  ancients  practically  as 
early  as  gold.  Silver  is  used  very  extensively  in  the  arts  and  sci- 
ences, as  in  jewelry,  tableware,  coinage,  silver  bullion  as  a  me- 
dium of  exchange,  photography,  mirrors,  for  optical  apparatus, 
in  plating  and  in  very  many  alloys.  Copper  lowers  the  melting- 
point  of  silver  and  makes  the  metal  harder,  but  does  not  decrease 
the  malleability,  or  materially  impair  the  color.  This  is  by  far 
the  most  important  of  the  silver  alloys,  and  in  coinage  nine 
parts  of  silver  to  one  part  of  copper  produces  a  coin  that  resists 
wear  through  friction.  Silver  mixes  with  lead  in  all  proportions 
when  molten  but  segregates  upon  cooling.  Therefore,  silver- 
lead  alloys  lose  their  homogeneity.  Silver  alloys  readily  with 
cadmium,  producing  a  soft,  white,  malleable,  and  ductile  alloy. 
Silver  alloys  readily  with  mercury  and  produces  silver  amal- 
gams. Silver  unites  with  tin,  zinc,  and  bismuth  in  the  forma- 
tion of  important  alloys,  generally  ductile  and  malleable.  With 
platinum,  silver  forms  a  hard  alloy,  that  is  used  very  extensively 
in  dentistry.  Silver  unites  with  palladium  and  with  rhodium; 
in  fact,  silver  unites  with  all  useful  metals  save  iron  and  cobalt. 


PLATINUM:  ITS  PROPERTIES,  OCCURRENCE  AND  USES 

Properties. — Platinum,  symbol  Pt,  is  one  of  the  rare  metals. 
It  has  a  specific  gravity  of  21. 46,  silver  white  with  a  grayish  tinge, 
ductile,  malleable,  sectile,  with  a  luster  less  brilliant  than  that 
of  silver.  Its  melting  point  is  1780°  C.  Its  atomic  weight  is 
195.  In  the  finely  divided  state  it  is  black.  The  presence  of 
minute  impurities  render  platinum  hard  and  brittle.  In  the 
electric  crucible  Moissan  volatilized  it,  but  its  boiling  point  is 
unknown.  It  is  unaffected  by  heat  in  both  dry  and  moist  air. 
It  is  insoluble  in  all  single  acids,  but  is  readily  soluble  in  aqua 
regia. 

Ores  of  Platinum. — Native  platinum;  sperrylite,  PtAs2,  which 
is  the  most  important  ore  of  the  metal;  platiniridium,  an  alloy 
of  platinum  and  iridium;  osmiridium,  an  alloy  of  osmium  and 
iridium;  native  osmium  and  irridium  contain  small  quantities 


PRECIOUS  METALS  103 

of  platinum;  it  occurs  in  covellite,  which  is  a  sulphide  of  copper, 
CuS;  and  in  laurite,  which  is  the  sulphide  of  ruthenium,  RuS2. 

Geographical  Distribution. — Platinum  occurs  in  small  quan- 
tities in  the  gold-bearing  sands  of  California  and  Oregon.  It 
occurs  in  limited  quantities  in  Arizona,  Colorado,  Georgia,  Idaho, 
and  Montana.  It  is  reported  from  Mexico,  Santa  Domingo, 
Brazil,  and  in  placer  deposits  in  Colombia.  The  world's  princi- 
pal supply  of  platinum  comes  from  the  Siberian  side  of  the  Ural 
Mountains.  In  Brazil  at  the  Congo  Soco  mines  it  occurs  in  the 
decomposed  schistose  rocks  associated  with  gold.  It  is  also 
found  in  small  quantities  in  the  placer  gravels  of  Alaska. 

The  platinum  production  in  the  United  States  has  come 
from  the  placer  mines  in  Butte,  Humboldt,  Siskiou,  Trinity, 
Calaveras,  Sacramento,  and  Del  Norte  Counties,  California. 
Three-fourths  of  the  amount  has  been  obtained  from  Butte 
County  alone. 

The  most  noteworthy  event  of  the  platinum  industry  in  recent 
years  is  the  discovery  of  the  comparatively  new  mineral,  sperry- 
lite,  the  arsenide  of  platinum,  PtAs2,  which  occurs  in  association 
with  nickel-bearing  ores  of  Sudbury,  Ontario,  and  in  the  Rambler 
mines,  Wyoming. 

Importance  is  also  attached  to  the  discovery  of  the  metal  in 
association  with  several  copper  minerals,  as  covellite,  the  sulphide 
of  copper,  CuS.  This  result  may  lead  to  the  discovery  of  plat- 
inum of  commercial  importance  in  other  members  of  the  copper 
group. 

With  the  present  high  price  of  platinum,  more  than  twice  the 
value  of  gold,  we  may  expect  a  persistent  search  for  platinum  ores : 
(1)  Among  the  placer  gravels  of  the  serpentine  rocks,  especially 
those  resulting  from  the  metamorphism  of  large  masses  of  per- 
idotite;  (2)  in  the  members  of  the  copper  group,  and  (3)  in 
the  nickeliferous  peridotites. 

Geological  Horizon. — Platinum  is  associated  with  the  pre- 
Cambrian,  Cambrian  and  Ordovician  terranes.  The  origin  of 
the  ore  bodies  is  largely  through  the  decomposition  of  the 
superincumbent  rocks,  which  allows  platinum  to  be  carried  into 
the  valleys  where  it  sinks  to  the  lower  portion  of  the  gravel  and 
into  the  cracks  and  the  crevices  of  the  upper  portion  of  the 
underlying  rock.  It  is,  therefore,  intimately  associated  with 
gold  in  placer  deposits,  and  may  be  reclaimed  by  the  same 
method  as  gold.  The  common  parent  rock  is  the  ultro-basic 


104  ECONOMIC  GEOLOGY 

ferro-magnesian  rock  known  as  peridotite.  Many  platinum 
placers  have  been  traced  back  directly  to  the  decomposition  of 
such  a  rock.  However,  all  peridotite  does  not  bear  platinum. 

Methods  of  Extraction. — (1)  By  placer  mining.  Platinum  is 
obtained  by  panning  the  lower  gravels  of  placers  or  by  hydraulic- 
ing  and  dredging  the  entire  gravels  of  the  larger  placers  for  the 
gold.  (2)  The  wet  method.  The  ores  of  platinum  are  treated 
with  hot  aqua  regia  which  dissolves  all  of  the  platinum  and  part 
of  the  iridium.  After  evaporating  the  excess  acid  the  platinum 
is  precipitated  by  ammonium  chloride  as  an  ammonium  chloro- 
platinate  (NH^PtCle.  Ammonium  chloride  and  chlorine  are 
volatile  upon  ignition  and  the  platinum  is  left  behind  as  a  spongy 
metal.  (3)  Recovery  from  waste  solutions.  The  waste  solution 
is  boiled  to  expel  any  excess  of  nitric  acid;  it  is  then  filtered  to 
remove  any  platinum  sponge  that  may  have  been  left.  Barium 
chloride  is  added  to  precipitate  any  sulphuric  acid  that  may  be 
present.  The  platinum  salts  now  in  solution  are  reduced  to  the 
elemental  state  by  concentrated  hydrochloric  acid  and  zinc. 
Electrolysis  may  be  substituted  in  place  of  zinc. 

Uses  of  Platinum. — According  to  Pliny,  platinum  was  known 
to  the  ancients,  for  it  occurred  in  many  alluvial  beds  associated 
with  gold,  and  remained  with  the  yellow  metal  after  the  washing 
of  the  gold.  In  1735  it  was  recognized  in  Columbia,  S.  A.  In 
1740  it  was  exported  from  Jamaica  to  Europe.  Near  the  middle 
of  the  eighteenth  century,  the  Spanish  government  forbade  its 
further  extraction  and  ordered  all  the  platinum  thrown  into  the 
seas  to  prevent  its  use  as  an  adulterant  of  gold.  In  1819  platinum 
was  discovered  in  serpentine  rocks  on  the  Siberian  side  of  the 
Urals.  Until  1823  the  world's  supply  of  platinum  came  solely 
from  South  America.  Since  1824  Russia  has  been  practically  the 
only  producer.  Platinum  was  used  by  the  ancients  as  an  adul- 
terant of  gold.  It  is  used  in  many  forms  of  chemical  apparatus 
in  which  a  high  melting-point  is  necessary.  It  is  the  only  avail- 
able metal  which  will  withstand  the  continuous  heat  of  baking, 
and  for  this  reason,  used  extensively  as  pins  to  hold  artificial 
teeth  together.  It  is  also  used  for  filling  teeth;  platinized  paper 
for  photographic  purposes;  jewelry,  and  in  coinage  when  alloyed 
with  2  per  cent,  of  iridium,  especially  in  Russia,  where  it  was  first 
introduced  in  1824,  on  account  of  its  malleability,  its  unadulter- 
ability,  and  its  intrinsic  value.  Platinum  is  also  used  in  the 
manufacture  of  contact  points  of  telegraph  keys;  for  stills  or 


PRECIOUS  METALS  105 

retorts  in  the  manufacture  of  crude  sulphuric  acid,  in  which  case 
it  is  alloyed  with  2  per  cent,  of  iridium.  On  account  of  its  infus- 
ibility  and  the  fact  that  its  coefficient  of  expansion  is  nearly  the 
same  as  glass,  platinum  is  used  to  connect  outside  copper  wires 
with  the  carbon  filament  in  incandescent  lamps.  The  thickness 
of  the  filament  varies  from  0.01  to  0.012  in.  Platinum  is  used  in 
the  manufacture  of  platinum  spoons,  dishes,  crucibles,  combs, 
foil  and  wire.  Liebig,  in  his  chemistry  letters,  states  that  with- 
out platinum  it  would  be  impossible  in  many  cases  to  make  an 
analysis  of  many  silicates,  and  thus  the  composition  of  most 
minerals  would  remain  unknown ;  without  platinum  the  composi- 
tion of  our  organic  compounds  would  likewise  remain  unknown. 
Platinum  is  used  extensively  by  balance  makers  for  weights ;  is 
used  in  surgical  and  scientific  instruments  of  precision;  for  the 
points  of  stylographic  pens;  for  the  balance  wheels  and  hair 
springs  of  non-magnetic  watches;  for  obtaining  a  silver  color  on 
porcelain;  for  platinum  plating;  for  oxidizing  silver;  for  the  fuses 
of  electrolytically  exploded  cartridges;  for  use  with  high-grade 
explosives  like  dynamite.  It  is  used  with  iridium  as  an  electrode 
for  the  electrolysis  of  alkaline  chlorides,  where  an  alloy  of  15  per 
cent,  of  iridium  can  be  rolled  to  a  thickness  of  0.007  of  a  milli- 
meter and  yet  have  sufficient  resistivity  to  be  used  on  an  indus- 
trial scale.  Platinum  is  used  also  in  the  manufacture  of  the 
platinum  salts  of  commerce.  It  is  also  used  in  the  making  of 
platinized  asbestos.  The  United  States  dental  and  electrical 
uses  of  platinum  equal  50  per  cent,  of  the  world's  output. 

The  Alloys  of  Platinum. — Platinum  alloys  readily  with  gold 
and  silver,  and  these  alloys  have  been  discussed  in  the  treatment 
of  silver.  Platinum  alloys  readily  with  copper  in  all  proportions 
at  high  temperatures.  The  alloys  are  extremely  hard  and  less 
liable  to  tarnish  than  the  ordinary  brasses  and  bronzes.  With 
81.25  per  cent,  copper  the  alloy  is  a  golden  yellow,  closely  resem- 
bling 18  carat  gold.  It  is  both  malleable  and  ductile  and  sus- 
ceptible of  a  high  polish.  Both  platinum  and  copper  alloy  read- 
ily with  about  4  per  cent,  of  zinc.  The  alloys  are  extensively  used 
in  jewelry;  mathematical  instruments,  and  chronometer  wheels. 
Platinum  bronze  is  an  alloy  of  platinum,  nickel,  and  tin.  With 
nickel,  platinum  forms  a  white,  malleable,  magnetic  alloy.  This 
is  capable  of  a  high  polish  and  is  permanent  in  moist  and  dry  air. 
The  presence  of  3  per  c.ent.  platinum  prevents  steel  from  rusting, 
and  is  therefore  of  great  industrial  importance  in  the  manufac- 


106  ECONOMIC  GEOLOGY 

ture  of  cutlery  and  instruments  of  precision.  The  alloys  of  plat- 
inum with  antimony,  arsenic,  bismuth,  cadmium  and  tin  are 
generally  brittle.  With  iridium  the  alloys  are  hard  and  elastic, 
permanent  in  moist  and  dry  air,  and  susceptible  of  a  high  polish. 
This  is  especially  true  when  less  than  25  per  cent,  of  iridium  is 
present.  Above  that  point  it  becomes  difficult  to  draw  the  alloy 
into  wire  or  to  hammer  it  into  sheets.  An  alloy  of  platinum  with 
10  per  cent,  of  iridium  resists  the  corrosive  action  of  metals  far 
better  than  pure  platinum.  It  has  been  stated  that  up  to  the 
beginning  of  the  present  century  25  per  cent,  of  all  platinum  used 
in  the  United  States  was  iridium.  We  use  alloys  of  platinum  and 
iridium  under  the  name  of  platinum.  Platinum  does  not  amal- 
gamate readily  with  mercury.  Here  it  is  unlike  gold  and  silver. 

Palladium. — Palladium,  symbol  Pd,  has  the  color,  luster  and 
appearance  of  platinum,  but  takes  a  finer  polish.  It  is  malleable 
and  ductile,  and  is  the  most  easily  fused  of  any  metals  of  the 
platinum  group.  It  is  usually  found  in  the  metallic  state,  some- 
times with  gold  and  silver,  and  also  associated  with  platinum  in 
the  ores  of  the  latter  metal.  Palladium  can  scarcely  be  distin- 
guished from  platinum  by  its  color.  It  is  chiefly  noted  for  its 
great  tendency  to  absorb  hydrogen.  It  is  with  difficulty  soluble 
in  nitric  acid.  It  dissolves  in  boiling  sulphuric  acid,  being  more 
easily  attacked  in  the  finely  divided  state.  It  melts  at  1586°  C., 
and  at  a  higher  temperature  yields  a  green  vapor.  It  forms  alloys 
with  gold,  silver,  copper,  mercury,  nickel,  antimony,  arsenic 
and  the  platinum  metals.  Palladium  is  used  chiefly  for  the  grad- 
uated surfaces  of  physical  instruments  and  for  coating  silver 
articles,  especially  mirrors,  because  it  retains  a  polish  and  does 
not  tarnish.  Its  atomic  weight  is  106.7. 

Osmium. — Osmium,  symbol  Os,  has  a  specific  gravity  of  22.47. 
It  is  a  bluish  metal,  harder  than  glass  and  infusible  in  the  oxyhydro- 
gen  flame.  It  crystallizes  in  cubes  or  rhombohedrons  and  is  the 
heaviest  of  all  known  solids.  It  burns  in  the  air  to  the  tetroxide, 
which  has  a  peculiar  penetrating  odor  and  is  injurious  to  the  eye. 
It  alloys  with  metals,  notably  iridium.  It  is  found  in  the  Ural 
Mountains,  Brazil,  California,  Borneo  and  Australia.  It  is 
used  in  pointing  gold  pens  and  as  bearings  for  compass  needles. 
Its  melting-point  is  2500°  C.  Its  atomic  weight  is  190.9. 

Iridium. — Iridium  has  a  specific  gravity  of  22.42  and  a  fusion- 
point  of  1950°  C.  It  is  a  hard,  white,  lustrous  metal  resembling 
steel.  It  is  malleable  at  red  heat.  It  melts  only  in  the  oxhy- 


PRECIOUS  METALS 


107 


drogen  flame.  It  is  brittle  and  very  hard.  It  is  a  powerful 
catalytic  agent  when  finely  divided.  It  is  obtained  by  igniting 
ammonium  chloriridate,  which  is  obtained  from  osmiridium  or 
the  platinum  residues  by  a  complicated  process.  It  is  found  in 
the  Ural  Mountains,  Brazil,  California,  Borneo  and  Australia. 
Its  atomic  weight  is  193.1. 

Rhodium. — Rhodium,  symbol  Rh,  is  a  white,  malleable,  ductile 
metal.  Its  specific  gravity  is  12.1  and  its  fusion-point  is  2000°  C. 
It  is  insoluble  in  acids  and  unchanged  in  air.  It  is  prepared  from 
platinum  residues  by  first  converting  it  into  rhodium  chloride 
and  then  by  reducing  this  by  heating  it  with  sulphur  in  a  carbon 
crucible.  It  forms  alloys  with  platinum,  gold,  bismuth,  and  lead. 
It  is  the  most  costly  of  all  the  metals,  being  worth  five  times  as 
much  as  gold.  It  occurs  in  small  quantities  in  platinum  ores  and 
in  some  native  gold.  It  is  found  in  the  Ural  Mountains  and  in 
Brazil.  Its  atomic  weight  is  102.9. 

METALS  OF  THE  PLATINUM  GROUP 


At.  wt. 

Sp.  gr. 

F. 

melting- 
point 

C. 

melting- 
point. 

Platinum  
Indium 

195.0 
193  1 

21.5 
22  33 

3225 

3892 

1780 
1950 

Osmium  
Palladium 

190.9 
106  7 

22.47 
11  4 

4532 
2732 

2500 
1586 

Rhodium  
Ruthenium  .  . 

102.9 
101.7 

12.1 
12.26 

3272 
3632 

2000 
1950 

The  members  of  the  platinum  group  occur  intimately  associated 
with  each  other.  Where  one  is  present  the  other  members  in 
larger  or  smaller  quantity  are  usually  present.  Native  platinum 
contains  from  16  to  40:  per  cent,  of  the  other  metals  of  the  group. 
These  often  alloy  with  each  other  as  in  iridosmine  and  platinirid- 
ium.  They  are  all  white  or  grayish-  white,  lustrous,  ductile  and 
malleable  metals.  They  are  all  permanent  in  the  ordinary  atmos- 
phere. Osmium  alone  burns  when  strongly  heated.  All  the 
others  are  scarcely  affected  by  oxygen  at  any  temperature.  Save 
palladium,  they  are  insoluble  in  any  single  acid,  and  often 
aqua  regia  is  without  solvent  action  upon  iridium  and  ruthenium. 
Palladium  fuses  at  the  temperature  of  wrought  iron,  and  is, 
therefore,  the  easiest  fused  of  any  members  of  the  group.  The 
order  of  fusibility  of  the  other  metals  is,  palladium,  platinum, 
ruthenium,  iridium,  osmium,  the  last  of  which  has  never  suffered 


108  ECONOMIC  GEOLOGY 

fusion.  All  these  minerals  occur  native  and  as  alloys,  principally 
as  scales  or  granules  in  the  placer  gravels,  in  the  same  location  as 
described  under  the  caption  of  platinum.  The  geological  horizon 
is  the  same  as  given  for  platinum. 

LOSSES  OF  PRECIOUS  METALS 

The  losses  of  precious  metals  may  be  classed  as  follows: 
(1)  Hoarding.  The  quantity  hoarded  is  indeterminable,  and 
the  loss  is  largely  retrievable.  (2)  The  amount  put  out  of  circu- 
lation as  objects  of  art  and  ornamentation.  (3)  Wear  and  tear. 
This  represents  an  irretrievable  loss.  It  occurs  in  the  wear  of  the 
coin  whereby  the  medium  of  exchange  to-day  meeting  the  stand- 
ard of  weight,  to-morrow  becomes  too  light,  as  its  edges  and  sides 
have  become  smooth.  The  coin  is  not  suitable  as  a  medium  of 
exchange,  and  it  goes  back  to  the  United  States  mint  for  recoin- 
age.  This  loss  also  occurs  in  the  gold  leaf,  silver  leaf,  wire,  and  in 
the  pure  metals  used  extensively  for  plating.  (4)  Loss  in  the 
useful  metals,  that  is,  ores  containing  too  low  a  percentage  of 
gold,  or  silver,  or  both,  to  separate  with  a  profit.  A  small  per- 
centage of  these  metals  goes  into  the  useful  metals  as  copper  and 
iron,  from  which  it  is  never  removed.  (5)  The  concentrates 
from  milling  processes  from  which  other  metals  are  recovered 
may  carry  so  small  a  percentage  of  either  gold  or  silver  that 
they  are  thrown  directly  into  the  waste,  thereby  losing,  for 
all  commercial  purposes,  a  certain  quantity  of  silver  and  gold. 
(6)  In  the  extraction  of  the  metals,  as  reducing  the  ore  to  a  pulp 
too  rapidly,  in  crushing  the  ore  too  coarsely  for  amalgamation 
to  take  place,  and  in  the  employment  of  cheap  labor.  (7)  Loss 
in  tailings.  In  some  plants  estimation  has  been  made  that  from 
50  per  cent,  to  60  per  cent,  of  the  actual  gold  and  silver  present 
in  the  ore  is  lost  in  the  tailings  from  the  mill.  If  the  loss  in  1 
gal.  of  water  is  0.018  cent,  and  if  576,000  gal.  of  water  per  day 
represents  the  amount  of  waste,  the  actual  loss  for  one  year  would 
be  represented  by  the  following: 

576,000  X  0.018  X  360  X  2  =  $74,649.60. 

(8)  By  crushing  the  ore  too  finely.  This  produces  a  flour  gold 
and  silver,  both  of  which  are  carried  away  on  the  surface  of  the 
water.  (9)  By  filling  the  holes  in  the  stamps  and  pans  with  amal- 
gam. (10)  By  cleaning  the  plates  too  quickly.  (11)  Byremov- 


PRECIOUS  METALS  109 

ing  the  amalgam  from  the  plates  too  thoroughly,  for  the  amalgama- 
tion is  not  complete  when  the  plates  are  new  or  perfectly  free  from 
the  amalgam,  that  is,  "  experienced "  plates  are  far  more  efficient 
in  the  extraction  of  the  gold  and  silver  than  the  "  inexperienced." 
(12)  By  using  too  slow  a  current  of  water.  If  the  current  be  too 
slow,  the  plates  become  covered  with  slime,  and  this  prevents  the 
gold  and  the  silver  from  coming  directly  in  contact  with  the 
amalgam.  (13)  By  using  too  rapid  a  current  of  water.  This  pre- 
vents the  metal  from  being  caught  on  the  amalgamating  plates, 
that  is,  the  heavy  current  of  water  simply  carries  it  away.  (14) 
By  not  keeping  the  mercury  clean.  This  prevents  the  amalgama- 
tion from  taking  place.  Whenever  mercury  is  covered  with  oil  from 
the  machinery,  or  oily  exudations  from  the  hands,  it  must  be  redis- 
tilled or  treated  with  lye  to  cut  the  oil.  (15)  By  the  flouring 
of  the  mercury,  that  is,  the  reduction  of  the  mercury  to  so  fine  a 
state  of  subdivision  that  it  will  not  adhere  to  the  amalgamating 
pans.  (16)  By  too  few  amalgamating  machines,  as  where  the 
ore  is  rich  and  the  quantity  required  to  pass  over  the  plates  is 
too  great  for  one  machine  to  do  the  work.  (17)  By  too  short 
sluices  or  plates;  by  using  the  blankets  too  long;  and  by  leaving 
the  plates  in  front  of  the  stamps  so  long  that  they  become 
charged  with  mud  and  other  debris  and  prevent  the  uniform 
feeding  of  the  gold  upon  the  amalgamating  plates. 


CHAPTER  IV 

USEFUL  METALS  (GROUP  I) 

LEAD  AND  MERCURY 

Properties. — Lead,  symbol  Pb,  is  a  soft,  bluish-white  metal. 
Its  freshly  cut  surface  has  a  bright  metallic  luster.  The  metal 
upon  exposure  quickly  becomes  coated  with  a  film  of  the 
oxide.  Lead,  unlike  the  other  metals,  is  sufficiently  soft  to  be 
scratched  with  the  thumb-nail.  It  even  leaves  a  lead  gray 
streak  upon  paper.  Lead  is  fashioned  into  foil  or  wire  by  rolling 
and  pressing.  It  is  readily  soluble  in  nitric  acid  but  the  other 
mineral  acids  are  without  special  solvent  effect  upon  the  metal 
at  ordinary  temperatures.  Its  specific  gravity  is  11.3.  Its 
melting-point  327°  C.  Its  atomic  weight  207.10. 

Ores  of  Lead. — Native  lead  occurs  in  small  quantities  in  many 
localities  both  in  the  United  States  and  in  foreign  countries.  It 
is  always  of  secondary  origin,  the  product  of  reduction  from  other 
lead  minerals  through  volcanic  action. 

Galenite,  PbS,  86.6  per  cent,  of  lead. 

Anglesite,  PbS04,  68.3  per  cent,  of  lead.  A  white  or  gray 
sulphate. 

Cerussite,  PbCOs,  77.5  per  cent,  of  lead.  A  white  or  pink 
carbonate. 

Pyromorphite,  3Pb3(PO4)2,PbCl2.  Often  in  small  hexagonal 
crystals. 

Cotunnite,  PbCl2,  74.5  per  cent,  of  lead. 

Massicot,  PbO,  92.8  per  cent,  of  lead.     A  buff  powder. 

Minium,  PbsO^  90.6  per  cent,  of  lead.     A  vivid  red  powder. 

Plattnerite,  Pb02,  86.6  per  cent,  of  lead.     An  iron  black  oxide. 

Crocoite,  PbCr04,  65  per  cent,  of  lead. 

Wulfenite,  PbMo04,  57  per  cent,  of  lead. 

Stolzite,  PbWO4,  44.9  per  cent,  of  lead. 

Galenite  is  by  far  the  most  important  ore  of  lead.  It  crystallizes 
in  the  isometric  system  in  perfect  cubes  and  regular  octahedrons. 
It  also  occurs  massive  and  granular.  Silver  sulphide,  Ag2S, 

110 


USEFUL  METALS  111 

is  often  intimately  associated  with  galenite  and  isomorphous 
with  it.  All  galenite  is  more  or  less  argentiferous  but  the  coarsely 
crystallized  variety  like  the  galenite  of  Rossie,  St.  Lawrence  Co., 
N.  Y.,  is  low  in  its  silver  content,  while  much  of  the  finely  crystal- 
lized galenite  of  the  Cordilleran  section  is  highly  argentiferous. 

The  last  seven  minerals  are  not  important  as  ores  of  lead,  but 
the  artificial  massicot,  minium  and  crocoite  are  important  in 
the  arts  and  industries.  Wulfenite  and  stolzite  are  interesting 
molybdenum  and  tungsten  salts  of  the  metal.  There  are  also 
many  compound  minerals  playing  only  a  minor  role  in  the  metal- 
lurgy of  the  metal. 

Origin  of  the  Ores. — As  already  noted,  native  lead  is  always  of 
secondary  origin,  the  direct  product  of  the  reduction  of  other 
ores.  The  sulphide  of  lead  is  precipitated  in  the  laboratory 
whenever  a  solution  bearing  H2S  comes  in  contact  with  neutral 
or  slightly  acid  solutions  bearing  lead  salts.  Galenite  appears 
to  have  been  formed  in  most  cases  from  mineralized  solutions 
by  hydro-chemical  reactions,  or  by  hydatogenetic  reactions  at 
temperatures  which  are  not  excessively  high.  Mayencon  has 
reported  galenite  as  a  product  of  sublimation  in  a  burning  coal 
mine,  Lacroix  and  Zambanini  both  report  galenite  as  a  Vesuvian 
sublimate  formed  during  the  eruption  of  April,  1906. 

Anglesite  is  a  common  oxidation  derivative  of  galenite  in  the 
presence  of  water  or  moist  atmosphere.  The  carbonate,  cerus- 
site,  is  derived  from  the  oxidation  of  other  ores  of  lead  in  the 
presence  of  carbonated  waters  in  the  upper  level  of  ore  bodies. 
Therefore  anglesite  and  cerussite  are  generally  present  in  the 
oxidized  zone  of  an  ore  body  bearing  lead  minerals.  The  rich- 
ness of  the  ore  varies  with  the  extent  of  the  decomposition  that 
has  taken  place.  If  it  is  limited  to  the  breaking  down  of  galenite 
the  ore  is  sometimes  very  rich.  If  the  associated  country  rock 
has  also  suffered  decomposition  the  ore  has  absorbed  so  much 
carbon  dioxide  in  the  formation  of  earthy  carbonates  that  it  is 
often  too  poor  in  lead  to  pay  for  profitable  extraction.  The 
oxides  are  always  of  secondary  origin  and  result  directly  from 
the  decomposition  and  reduction  of  Other  lead  minerals.  The 
chloride  of  lead,  cotunnite,  is  a  volcanic  mineral  produced  by 
sublimation. 

Character  of  the  Ore  Bodies. — Primary  galenite  appears  to 
be  connected  with  the  acid  intrusives  of  all  ages.  Minerals 
which  characterize  ores  of  pneumatolytic  origin  are  absent  and 


112 


ECONOMIC  GEOLOGY 


the  galenite  is  hydatogenetic  (Fig.  70).  According  to  Thomas  and 
MacAlister  the  Derbyshire  galenite  assumes  a  variety  of  forms 
which  they  have  classified  as  rakes,  pipes,  flats  and  serins.  The 


FIG.  70. — Section  exposed  in  a  breast  of  the  Enterprise  mine  at  Rico, 
Dolores    County,    Colorado.     (After    Rickard.} 

rakes  are  true  fissures,  often  faults;  the  serins  are  mineralized 
fissures  crossing  them;  the  flats  are  mineralized  bedding  planes; 
the  pipes  are  irregular  pipe-like  bodies  of  ore. 


FIG.  71. — Ideal  section  through  flats  and  pitches  of  the  lead  and  zinc  region 
of   Wisconsin.     (After   Chamberlain.} 

In  the  United  States,  lead  minerals  occur  in  veins  which  may  be 
tilted  to  almost  any  angle  with  the  strata  which  the  fissure  vein 
traverses.  In  Missouri,  galenite  occurs  filling  large  cavities  as 


USEFUL  METALS 


113 


chamber  deposits  and  as  gash  veins;  also  it  occurs  in  what  is 
known  as  flats  and  pitches.     (See  Fig.  71.) 

The  most  important  lead  deposits  of  the  United  States  are  of 


:?-.'s :  Vy*  ££  ffiffiffifr* Pf 


~-  SO  I  LAND  RESIDUARY  OAY 
UPPER  GALENA 

-"-  MIPPLE  GALENA 

LOWER  GALENA 
BLUE  L1ME5TOME, 
LIMESTONE 
PETER'S  5ANDSTQNE 


FIG.  72. — Ideal  section  in  the  lead  and  zinc  region  of  Wisconsin,  showing 
the  forms  of  ore  deposits  at  the  different  horizons.     (After  Chamberlain.) 


Greywackt    Diorite        Colette,        Quartz        Galena        Blendi 


FIG.  73. — Section   of  the   Adelbert  lodes,   Pribam,  Bohemia.     (After  J, 

Zadrizil.) 

metasomatic  origin.  They  occur  in  the  limestones  of  all  ages 
(Fig.  72).  Fossils  have  been  replaced  by  galenite  retaining  both 
the  external  form  and  internal  structure  of  the  organism.  Such 


114  ECONOMIC  GEOLOGY 

instances  have  been  reported  from  Sardinia,  England,  and 
Westphalia. 

The  mineralizing  solutions  in  most  cases  of  metasomatic  galen- 
ite  belong  to  the  descending  ground-water  currents.  There  are, 
however,  examples  of  metasomatic  replacement  deposits  that  have 
resulted  from  the  action  of  heated  solutions  rising  from  below 
in  accordance  with  the  theory  of  the  ascensionists.  Both  of  these 
deposits  usually  occur  in  limestones  which  interact  upon  percola- 
ting waters  charged  with  solutions  of  lead  salts.  The  limestones 
did  not  originally  contain  the  galenite.  Its  source  was  some 
associated  igneous  rock  or  sulphide-bearing  sediment.  Alkaline 
sulphides  may  have  aided  in  effecting  the  solution  of  the  lead,  and 
the  lead  in  solution  was  doubtless  transported  as  a  sulphide  and 
deposited  in  the  place  of  the  dissolved  limestone. 

Galenite  is  usually  associated  with  several  other  minerals, 
common  among  which  are  calcite,  dolomite,  siderite,  sphalerite, 
pyrite,  rhodonite  and  quartz,  as  shown  in  Fig.  73. 

Geographical  Distribution. — Lead  in  its  various  ores  is  widely 
distributed.  The  mineral  galenite  is  found  in  almost  all  countries, 
but  few  are  of  great  importance.  It  occurs  in  the  United  States, 
England  and  Sweden  in  limestones.  In  the  Harz  Mountains 
it  occupies  veins  in  clay  slate;  in  Freiberg  it  occurs  in  veins  in 
gneiss;  in  Spain  as  veins  in  granite. 

The  United  States  is  the  largest  producer  of  lead.  The  Ameri- 
can area  may  be  divided  into  three  distinct  fields:  the  Appala- 
chian; the  Missippi  River  belt,  and  the  Cordilleran  region. 

(1)  The  first  district  is  of  the  least  importance.  It  extends 
from  Alabama  on  the  south  to  Maine  on  the  north.  The  ores 
are  associated  with  Cambrian  or  Cambro-Ordovician  metamor- 
phics.  The  belt  comprises  a  highly  folded  and  often  faulted 
series  of  crystalline  schists  and  limestones.  In  Pennsylvania 
galenite  occurs  in  many  places  in  these  crystallines  and  is  often 
argentiferous,  varying  from  $2  to  $2000  per  ton  in  silver.  Lan- 
caster, Chester,  Northumberland  and  Wayne  Counties  are  most 
important  sections.  In  New  York,  at  Rossie,  St.  Lawrence  Co., 
galenite  occurs  in  veins  3  or  4  ft.  in  width.  The  crystals  are 
often  very  large  and  assiciated  with  a  calcite  gangue.  In  Vir- 
ginia the  terranes  associated  with  lead  at  Austin's  Mines  and 
Sterling  are  Cambrian  and  Ordovician.  It  is  not  likely  that  any 
of  these  localities  in  the  Appalachain  belt  will  ever  become  great 
producers  of  this  useful  metal  (Fig.  74). 


USEFUL  METALS 


115 


(2)  The  Mississippi  River  belt  comprises  the  following  states : — 
Minnesota,  Missouri,  Illinois,  Iowa,  Kansas,  Kentucky,  and  Ar- 
kansas. The  Missouri-Kansas  district  is  the  most  important  of 
them  all.  It  is  further  divided  into  three  distinct  fields:  (a) 
The  southeast;  (b)  the  central;  and  (c)  the  southwest.  In 
the  first  two  fields  the  ore  is  distinctively  galenite.  In  the  third 
district  the  ore  is  associated  with  zinc. 

Joplin  is  in  the  southwest  district.  The  ore  occurs  in  lime- 
stones and  chert  of  Mississipian  age  intimately  associated 


FIG.  74. — Open  cut  in  barren  ground  near  lola,  Marion  County, 
Arkansas,  showing  jointed  dolomite.  (After  G.  I.  Adams,  U.  S.  Geological 
Survey.) 

with  the  slates  and  shales  of  the  Coal  Measures.  The  ore 
bodies  are  often  massive  and  sometimes  hundreds  of  feet  in 
diameter.  The  ore  occurs  massive  and  granular  and  in  crystals 
of  the  isometric  system.  The  associated  minerals  are  chert, 
calcite,  dolomite,  barite  and  pyrite.  These  are  all  of  secondary 
origin.  The  country  rock  is  sometimes  massive  and  sometimes 
fragmental  (Fig.  75).  In  this  district  the  ore  is  associated  with 
sphalerite,  ZnS,  which  sometimes  has  a  resinous  luster;  sometimes 
it  is  the  ferriferous  sphalerite,  containing  10  per  cent,  or  more  of 


116 


ECONOMIC  GEOLOGY 


iron  and  known  by  the  miners  as  black  jack.  Calamine,  the 
hydrous  silicate  of  zinc,  and  smithsonite,  the  carbonate  of  zinc, 
appear  as  associated  minerals.  Both  of  these  are  classified  in  the 


trade  as  silicates.  The  lenticular,  tabular  and  cylindrical  forms 
are  more  common  in  the  southeastern  and  central  districts  than 
in  the  southwestern. 


USEFUL  METALS  117 

In  the  Doe  Run  mine  in  southeast  Missouri,  the  ore  is  galenite 
in  limestone.  The  ore  body  is  sometimes  from  50  to  90  ft.  in 
diameter.  It  is  generally  in  layers  parallel  to  the  stratification, 
but  sometimes  in  vertical  or  inclined  seams  and  occasionally  dis- 
seminated through  the  limestone  with  calcite  and  nickeliferous 
pyrite,  bearing  pyrite  or  pyrrhotite  as  accessory  minerals.  The 
sedimentaries  rest  unconformably  upon  Archean  granite  and 
gneiss.  Mine  La  Motte,  Bonne  Terre,  and  Doe  Run  are  the 
most  important  mines  in  this  district. 

In  southern  Illinois  and  Kentucky  the  gangue  mineral  is 
fluorite,  which  is  occasionally  mined  and  sold  to  iron  blast- 
furnace operators. 

(3)  The  Cordilleran  District:  In  Colorado,  Leadville  is  the 
most  important  locality.  Here  the  galenite  is  oxidized  at  the 
surface  and  is  argentiferous.  The  associated  rocks  are  Lower 
Carboniferous  limestones  and  dolomites,  Ordovician  limestones 
and  dolomites,  and  Cambrian  quartzites  resting  on  Archean 
granite.  These  terranes  are  all  traversed  by  sheets  and  dikes  of 
Cretaceous  and  post-Cretaceous  age.  The  white  and  gray  por- 
phyries are  older  and  more  important.  The  main  ore  body  lies 
in  the  limestone  of  the  Lower  Carboniferous  age.  The  blue  lime- 
stone at  or  near  its  contact  with  the  Leadville  porphyry  is  the 
most  important  horizon.  According  to  S.  F.  Emmons,  they  con- 
stitute a  contact  sheet,  whose  upper  surface,  formed  by  the  base 
of  the  porphyry  sheet,  is  comparatively  regular  and  well  defined. 
The  lower  surface  is  irregular  and  ill  defined.  There  is  a  gradual 
transition  from  ore  into  unaltered  limestone.  The  ore  sometimes 
occupies  the  entire  thickness  of  the  blue  limestone.  (See  Fig.  76.) 

The  ore  also  occurs  in  irregularly  shaped  bodies  or  in  transverse 
sheets  not  always  connected  with  the  upper  or  contact  surface  of 
the  ore-bearing  bed  or  rock.  It  also  occurs  sometimes  at  or  near 
the  contact  of  sheets  of  gray  or  other  porphyries  with  the  blue 
limestone.  Less  frequently  it  occurs  in  both  the  calcareous  and 
siliceous  sedimentaries.  According  to  Hancock  the  main  mass 
of  the  argentiferous  galenite  lies  in  the  limestones  and  dolomites 
while  the  ores  containing  gold  and  copper  are  more  pronounced 
in  the  siliceous  beds,  in  porphyries  and  in  the  crystalline  rocks. 

From  an  economic  standpoint,  the  most  important  mineral 
is  the  argentiferous  galenite  with  its  secondary  cerussite  and 
cerargyrite.  Lead  also  occurs  here  as  the  sulphate,  anglesite, 
as  the  phosphate,  pyromorphite,  and  in  the  form  of  the  oxides 


118 


ECONOMIC  GEOLOGY 


massicot  and  minium.  Native  silver  and  embolite  are  both  as- 
sociated with  the  Leadville  ores.  The  gangue  minerals  are  quartz, 
siderite,  pyrite  and  gypsum. 

S.  F.  Emmons  in  Monograph  XII  of  the  United  States  Geologi- 
cal Survey  Reports  states: 

"  That  the  ores  must  have  been  formed  beneath  a  thickness  of  at  least 
10,000  ft.  of  superincumbent  rocks  and  an  unknown  amount  of  sea 
water.  If  they  had  been  deposited  from  hot  ascending  solutions  as  the 
result  of  the  relief  of  pressure,  it  would  naturally  be  expected  that  the 


FIG.  76. — Map  showing  approximate  distribution  of  the  principal 
silver,  lead  and  gold  regions  of  Colorado.  After  Spurr.  (By  permission 
of  the  Macmillan  Company,  from  Ries'  Economic  Geology.) 

bulk  of  the  deposit  would  have  been  found  in  the  upper  part  of  this  mass 
of  rocks  where  the  pressure  was  least  instead  of  at  its  base.  If  the  de- 
posits had  been  made  from  ascending  currents,  it  would  naturally  be 
expected  that  the  process  of  deposition  should  have  acted  from  the 
lower  surface  of  the  beds  upward,  instead  of  from  the  upper  surface 
downward,  as  is  shown  in  the  case  of  the  blue  limestone  which  carries 
the  bulk  of  the  ores.  The  few  approximately  vertical  ore  bodies  that 
have  come  under  observation  afford  no  evidence  that  their  walls  form 
part  of  a  channel  through  which  the  ore  currents  came  up  from  below. 
A  downward  current  seems  best  to  suit  the  facts  thus  far  observed  in  the 
Leadville  deposits." 


USEFUL  METALS  119 

The  ore  therefore  seems  to  have  been  derived  from  the  porphy- 
ries by  leaching  and  deposited  in  the  limestone  by  metasomatic 
replacement.  The  aqueous  solutions  traversing  the  joint  planes 
and  bedding  planes  of  the  limestone  deposited  the  ore  in  later 
Cretaceous  times. 

Newbery  and  LeConte  have  suggested  that  the  ores  were  derived 
from  ascending  solutions  bearing  lead  salts  or  ores  consisting  of 
cerussite  (the  carbonate),  galenite  (the  sulphide),  and  anglesite 
(the  sulphate)  of  lead  (Fig.  77). 

Aspen  is  another  important  locality  in  Colorado  in  which  is 


FIG.  77. — General  view  of  Rico,  Colorado,  and  Enterprise  group  of 
mines.  (By  permission  of  the  Macmillan  Company,  from  Hies1  Economic 
Geology.) 


found  argentiferous  lead  ores.  According  to  H.  Ries,  the  ores  are 
oxidized  and  occur  in  folded  and  faulted  Carboniferous  limestone, 
although  the  section  involves  rocks  ranging  from  the  Archean  to 
the  Mesozoic  in  age.  Two  quartz  porphyries,  one  at  the  base  of 
the  Devonian  and  the  other  in  the  Carboniferous  at  present  ap- 
pear to  bear  no  special  relation  to  the  ore  bodies. 

At  the  close  of  the  Cretaceous  the  rocks  were  folded  into  a  great 
anticline,  with  a  syncline  on  its  eastern  limit.  Contemporaneous 
with  the  folding  there  were  produced  two  faults  parallel  with  the 
bedding  of  the  Carboniferous  dolomite.  At  the  same  time  much 


120 


ECONOMIC  GEOLOGY 


cross  faulting  occurred.  The  ore  is  found  chiefly  at  the  intersec- 
tion of  these  two  sets  of  fault  planes. 

According  to  J.  E.  Spurr,  the  ores  were  deposited  by  magmatic 
waters  ascending  vertically  along  these  faults  and  were  precipi- 
tated by  the  reaction  between  the  solutions  and  certain  wall  rocks, 
chiefly  shales.  The  mingling  of  solutions  at  the  intersection  of 
the  fissures  also  played  an  important  role  in  the  formation  of  the 
ore  bodies. 

According  to  W.  H.  Weed,  the  richer  ore  at  the  intersection  of 


>Sv/:::;^^^ 
/•A:'\v/^-/'|.v./:-v 


FIG.  78. — Sketch  showing  structure  of  Silver  Shield  lode,  northeast  face  of 
stope.     (After  J.  M.  Boutwell,   U.  S.  Geological  Survey.} 

these  fault  planes  was  due  to  secondary  deposition,  while  Spurr 
finds  little  evidence  of  secondary  sulphide  formation.  The  ores 
are  peculiarly  free  from  other  metals  (Fig.  78). 

In  Utah  and  Nevada,  argentiferous  galenite  yields  much  lead 
as  a  by-product  (see  chapter  on  the  precious  metals).  In  Idaho 
the  bulk  of  the  lead  has  been  from  the  Coeur  d'Alene  district 
in  Shoshone  County.  This  district  has  for  many  years  been 
one  of  the  leading  lead-producing  sections  of  the  country.  The 


USEFUL  METALS 


121 


FIG.  79. — Map  showing  location  of  Coeur  d'  Alene,  Idaho  district. 
After  Ransome.  (By  permission  of  the  Macmillan  Company,  from  Ries' 
Economic  Geology.} 


Areas  in  which  occur     Areas  in  which  occur       Area  in  which        Principal  auriferous     Productive  minos       Prospects  or  mine* 
lead-silver  deposits  of    lead-silver  deposits  of         occur  cppper  areas  not  of  primary 

known  primary         secondary  importance  deposits  importance' 

importance  so  far  as  at  present 

known 

FIG.  80. — Geologic  map  of  Coeur  d'  Alene,  Idaho  district.  (After 
Ransome.  (By  permission  of  the  Macmillan  Company,  from  RiesJ  Economic 
Geology.) 


122  ECONOMIC  GEOLOGY 

Bunker  Hill  Mine,  The  Federal  Mining  and  Smelting  Company, 
and  the  Hercules  Mine  are  some  of  the  principle  producers. 
Ninety-nine  per  cent,  of  the  lead  and  the  same  per  cent,  of  the 
silver  in  the  Coeur  d'Alene  District  comes  from  the  Revette 
quartzite  and  Burke  sandstones,  quartzites  and  shales  (Figs.  79 
and  80). 

According  to  F.  L.  Ransome,  there  are  no  sediments  in  the  dis- 
trict younger  than  the  Algonkian,  except  the  fluviatile  deposits 
some  of  which  may  be  of  Tertiary  age.  The  post-Algonkian 
intrusives  are  monzonite  and  syenite.  The  ore  deposits  of  the 
district  are  divided  into  three  classes:  (1)  Lead-silver  deposits; 
(2)  gold  deposits,  and  (3)  copper  deposits. 

The  lead-silver  deposits  occur  in  metasomatic  fissure  veins 
formed  largely  by  replacement  along  zones  of  fissuring  or  of  com- 
bined fissuring  and  faulting,  and  partly  by  the  filling  of  open 
spaces.  The  ore  bodies  are  tabular  and  the  mineralized  fissures 
have  the  characteristics  of  faults.  They  differ  from  the  great 
faults  of  the  region  in  that  the  more  important  faults  are  not  ore 
bearing.  Fissuring  and  cleavage  are  so  closely  related  to  each 
other  that  the  structure  may  be  termed  a  shear  zone.  Ries  con- 
siders that  the  metamorphism  was  adequate  to  produce  new 
minerals.  The  most  characteristic  minerals  are  galenite  and 
siderite,  the  carbonate  of  iron.  Sometimes  the  galenite  replaces 
the  sericitic  quartzite.  Sometimes  the  quartzite  is  replaced  by 
siderite  and  in  turn  by  galenite. 

The  galenite  was  not  all  deposited  during  one  period  for  some- 
times the  masses  of  coarsely  crystallized  galenite  is  traversed  by 
veinlets  of  a  more  compact  variety  of  the  same  mineral.  The 
lead  minerals  found  in  the  oxidized  zone  are  cerussite  and  pyromor- 
phite ;  the  silver  minerals,  native  silver  and  cerargyrite ;  the  copper 
minerals,  azurite  and  malachite ;  and  the  hydrated  oxide  of  iron, 
limonite. 

Geological  Horizon. — Lead  minerals  are  not  confined  to  any 
geological  horizon.  They  occur  widely  distributed  in  the  rocks 
of  all  ages.  They  are,  however,  most  abundant  in  the  Cambrian, 
Ordovician,  Carboniferous,  and  Cretaceous  ages. 

Extraction  of  the  Metal.  (1)  The  Reduction  Process. — Lead 
oxides  are  readily  reduced  to  the  metallic  state  by  carbon  accord- 
ing to  the  equation  PbO+C  =  Pb+CO. 

(2)  The  Roast-reaction  Process. — The  ore  is  crushed  and  intro- 
duced into  a  reverboratory  furnace  in  small  quantities.  The  ore 


USEFUL  METALS  123 

is  first  oxidized  to  the  sulphate  according  to  the  equation  PbS+ 
202  =  PbSO4.  The  oxygen  acting  upon  the  lead  sulphate  formed 
in  the  presence  of  a  new  charge  of  ore  reduces  the  sulphate  to  the 
oxide.  The  oxide  reacts  also  upon  a  new  charge  of  ore  when 
some  metallic  lead  is  formed  and  sulphur  dioxide  is  set  free  ac- 
cording to  the  equation  2PbO+PbS  =  Pb+SO2.  The  reduced 
metal  sinks  to  the  bottom  of  the  furnace,  runs  through  an  inclined 
trough  into  an  iron  kettle  from  which  the  metal  is  dipped  into 
moulds.  The  process  is  applicable  to  galenite  that  is  fairly  free 
from  the  sulphides  of  the  heavy  metals. 

(3)  The  Precipitation  Process. — In  this  process  the  ores  may  be 
charged  in  the  raw  state  into  a  blast-furnace  or  calcined  to  remove 
volatile  acid  radicles  or  impurities.     If  the  ore  is  the  sulphate, 
anglesite,  it  will  produce  lead  oxide  and  sulphur  trioxide,  thus: 
PbSO4  =  PbO  +  S03.     If  the  ore  is  the  carbonate,  cerussite,  it  will 
yield  lead  oxide  and  carbon  dioxide,  PbC03  =  PbO+CO2.     If  the 
ore  is  the  sulphide,  galenite,  it  will  yield  lead  oxide  and  sulphur 
dioxide,  PbS  +  30  =  PbO  -f  SO2     If  the  ore  be  the  oxidation  prod- 
uct, massicot,  some  volatile  impurities  may  be  removed.     The 
oxide  is  then  introduced  into  a  blast-furnace  with  coke,  scrap  iron, 
or  the  sulphide  of  iron.     At  a  high  temperature  the  entire  mass 
is  melted.    The  silicate  of  iron  rises  to  the  surface  as  a  slag  and  may 
be  drawn  off  as  in  ordinary  copper  smelting.    The  sulphides  of  iron, 
tin,  antimony,  and  copper,  will  be  formed  provided  these  metals 
are  present  and  may  be  drawn  off  at  a  lower  level.     The  sulphides 
often  found  are  the  black  sulphide  of  copper,  CuS,  the  sulphide 
of  antimony,  Sb2Ss,  of  tin,  SnS,  and  of  iron,  FeS.     At  the  bottom 
of  the  furnace  is  found  the  metallic  lead.     An  equation  represent- 
ing the  reduction  to  the  elemental  state  in  the  presence  of  iron 
would  be  PbS  +  Fe  =  FeS + Pb.     The  lead  thus  obtained  is  impure 
and  is  subsequently  refined.     If  it  contains  silver  in  commercial 
quantities  the  lead  is  desilverized  by  the  Pattinson  process. 

(4)  The  Lime-roasting  Process. — This  method  is  comparatively 
new  and  depends  upon  the  treatment  of  galenite  with  lime  or  gyp- 
sum under  conditions  favorable  for  oxidation.     The  percentage  of 
lead  and  silver  saved  by  this  method  is  said  to  be  larger  than  that 
obtained  by  the  preceding  method  while  the  cost  of  treatment  is 
no  greater. 

Uses  of  Lead. — One  of  the  most  important  uses  of  lead  is  in 
the  manufacture  of  white  lead.  Lead  is  used  also  in  the  manu- 
facture of  other  lead  pigments  under  the  name  of  litharge,  red  lead, 


124  ECONOMIC  GEOLOGY 

orange  mineral  and  sublimed  blue  lead.  Lead  is  used  in  the  manu- 
facture of  lead  pipe,  shot,  etc.,  and  in  many  alloys  that  are  of  great 
commercial  significance.  Sheet  lead  is  used  extensively  for  lin- 
ings to  withstand  the  corrosive  action  of  acids  or  acid  vapors.  In 
the  manufacture  of  sulphurous  and  sulphuric  acid  the  chambers 
and  towers  are  lined  with  sheet  lead.  Lead  is  also  used  for  the 
barrels  utilized  in  the  chlorination  of  gold  and  for  the  linings  of 
many  vats.  In  former  years  sheet  lead  was  used  for  roofing  and 
for  jointing  but  other  metals  have  largely  taken  its  place.  It  has 
been  used  in  the  glazing  of  windows,  and  now  an  exceedingly  im- 
portant use  is  for  coverings  for  electric  cables.  This  use  perhaps 
more  than  any  other  is  responsible  for  the  increasing  domestic 
consumption. 

Shot  was  early  manufactured  in  Missouri  and  Wisconsin.  Pos- 
sibly this  is  the  earliest  use  of  lead  in  America.  In  times  of  peace 
and  war  a  continuance  of  that  use  is  very  important.  Lead  is 
used  also  in  storage  batteries  and  in  many  forms  of  chemical  works. 
Among  the  alloys  type  metal,  britannia  ware,  and  the  various 
form  of  babbitt  known  as  antifriction  alloys  are  exceedingly  im- 
portant. It  is  used  also  in  the  various  grades  of  solder  as  fine, 
medium  and  coarse;  in  the  composition  of  organ  pipes;  in  the  fus- 
ible alloys  used  in  electric  lighting  systems;  in  fireprotection 
sprinklers  and  in  alloys  with  the  precious  metals,  some  of  which 
are  of  commercial  significance. 

White  lead  is  the  most  important  of  the  lead  pigments.  It  is 
used  directly  as  a  pigment  and  as  a  source  of  other  pigments. 
White  lead  has  to  meet  the  competition  of  zinc  white  .and  heavy 
spar.  These  three  pigments  are  sometimes  used  together.  Ninety 
per  cent,  of  all  the  white  lead  of  commerce  is  manufactured  by 
the  Dutch  process  at  New  Kensington,  Pa.,  by  the  Sterling  White 
Lead  Company.  Their  product  is  surpassed  by  none  in  its  opac- 
ity, its  covering  power,  and  in  its  durability  as  a  pigment.  The 
process  is  based  upon  the  fact  that  acetic  acid  has  a  strong 
corrosive  effect  upon  lead.  The  lead  is  therefore  immersed  for 
several  months  in  dilute  acetic  acid  or  vinegar,  when  in  the 
presence  of  carbon  dioxide  and  heat  the  corrosion  is  complete. 
The  liquid  is  drawn  off.  The  residue  is  placed  in  drying  rooms 
which  are  of  the  filter  type  not  used  elsewhere  in  the  world.  The 
heat  required  in  drying  is  small,  only  enough  to  remove  what 
moisture  cannot  pass  through  the  filters.  Chestnut  and  oak 
bark  are  used  in  the  process.  The  bark  is  exhausted  only  to  its 


USEFUL  METALS  125 

most  effective  point.  The  spent  tan  resulting  therefrom  is 
of  superior  quality  and  its  concentrated  extract  is  sold  to  the 
leather  tanneries. 

Litharge  is  another  important  lead  pigment.  Its  most  impor- 
tant use  is  that  of  a  pigment.  It  is  used  also  as  an  ingredient  in 
the  compounding  of  rubber,  in  the  manufacture  of  glass,  in  assay- 
ing, mixed  with  glycerine  to  hold  pipes  and  table  tops  together. 
It  may  be  manufactured  from  several  lead  salts  by  roasting  them 
to  drive  off  the  volatile  acid  radicle.  The  powder  obtained  is  a 
buff  yellow,  but  if  heated  to  the  point  of  fusion  reddish-yellow 
scales  of  the  oxide  appear.  This  product  is  known  in  the  marts 
of  trade  as  litharge.  It  is  obtained  in  large  quantities  during  the 
desilverization  of  lead. 

Another  lead  pigment  of  considerable  importance  is  red  lead. 
It  is  not  only  used  as  a  pigment  but  also  in  the  manufacture  of 
flint  glass,  and  very  extensively  in  the  production  of  structural 
steel.  It  is  also  used  as  a  pipe-joint  cement.  It  can  be  manu- 
factured by  heating  for  a  considerable  time  various  salts  of  lead 
at  a  temperature  of  450°. 

Orange  mineral  is  another  lead  pigment  of  less  commercial 
significance.  It  can  be  manufactured  by  the  treatment  of 
soluble  salts  of  lead  with  sodium  oxy chloride  in  the  presence  of  an 
alkaline  hydrate. 

Sublimed  blue  lead  is  obtained  as  a  by-product  in  the  sublima- 
tion of  galenite  and  consists  of  a  mixture  of  lead  oxide,  lead 
sulphide,  lead  sulphite,  zinc  oxide  and  carbon.  It  is  used  in  the 
manufacture  of  rubber  goods. 

Lead  arsenate  is  used  also  in  the  destruction  of  the  gypsy  moth. 

The  production  of  lead  includes  base  bullion,  pig  lead,  bars, 
sheets  and  old  lead.  Pig  lead  is  reported  by  all  smelters  operating 
in  the  Mississippi  Valley.  Refined  lead  embraces  all  of  the  de- 
silverized lead  produced  in  this  country,  and  the  pig  lead  recov- 
ered from  the  Mississippi  Valley  lead  industry.  Antimonial  lead 
is  derived  from  the  treatment  of  gold  and  silver  ores  bearing 
antimony.  In  the  process  of  extraction  of  the  precious  metals 
the  antimony  combines  with  the  lead  in  the  formation  of  anti- 
monial  lead.  For  this  product  there  is  quite  a  large  demand 
and  the  two  metals  are  never  separated. 

In  1885  there  began  in  the  United  States  the  treatment  of  for- 
eign ores  and  base  bullion  largely  from  Mexico.  Part  of  this  prod- 
uct is  smelted  and  exported,  but  a  considerable  quantity  is  con- 


126  ECONOMIC  GEOLOGY 

sumed  at  home.  Some  lead  is  brought  in  duty  free.  This  has 
considerable  influence  upon  the  annual  statistics  of  the  metal. 
The  total  valuation  of  metallic  lead  and  all  the  pigments  derived 
therefrom  has  in  some  years  exceeded  $60,000,000. 

Mercury :  Its  Properties,  Occurrence  and  Uses. 

Properties. — Mercury,  symbol  Hg,  is  a  bright,  silver  white, 
metal,  liquid  at  ordinary  temperatures.  It  was  this  physical 
property  that  gave  the  metal  the  old  name  of  quicksilver.  It 
is  the  only  metal  liquid  at  ordinary  temperature.  Bromine  is 
the  only  other  element  liquid  at  normal  temperature.  At  38.8° 
below  zero  mercury  crystallizes  in  the  isometric  system.  The 
malleable  and  ductile  cubes  are  of  higher  specific  gravity  than 
the  liquid  metal.  The  liquid  metal  emits  vapor  at  ordinary 
temperatures.  It  does  not  tarnish  upon  exposure.  It  is  not 
attacked  by  HC1,  nor  by  concentrated  ^H^SO 4  without  heat. 
It  is  readily  soluble  in  HNOs.  Its  specific  gravity  as  a  liquid 
is  13.59,  as  a  solid  it  is  14.19.  Its  boiling  point  is  357°.  Its 
atomic  weight  is  200. 

Ores  of  Mercury. — Native  mercury,  Hg,  is  rare  but  sometimes 
reported  in  considerable  quantity. 

Cinnabar,  HgS,  86.2,  per  cent,  of  mercury.  The  only  cochineal 
red  mineral  entirely  volatile  before  the  blowpipe. 

Metacinnabarite,  86.2  per  cent,  of  mercury.  The  black  sul- 
phide of  mercury. 

Calomel,  HgCl,  84.9  per  cent,  of  mercury.  Most  abundant 
in  Carniola  and  Spain. 

Tiemannite,  HgSe,  71.7  per  cent,  of  mercury.  The  selenide 
of  mercury  which  was  once  worked  in  the  Lucky  Boy  claim  in 
Utah. 

Living stonite,  HgS,2Sb2S3,  24.8  per  cent,  of  mercury.  A 
double  sulphide  of  mercury  and  antimony  that  has  furnished  a 
small  amount  of  the  metal  in  Mexico. 

Amalgam,  HgAg,  is  an  alloy  of  silver  and  mercury  in  varying 
proportions.  The  mercury  may  be  as  low  as  5  per  cent,  or  as 
high  as  73.6  per  cent. 

Origin  of  the  Ores. — Mercury,  unlike  the  precious  and  most 
of  the  useful  metals  is  not  very  abundant  nor  widely  diffused 
in  nature.  It  must,  however,  be  remembered  that  owing  to  its 
volatility  minute  traces  of  the  metal  may  be  easily  overlooked. 


USEFUL  METALS  127 

Native  mercury  occurs  in  small  globules  scattered  through 
cinnabar  and  metacinnabarite  as  a  product  of  reduction  by 
organic  matter.  Bituminous  substances,  as  idrialite  and  napa- 
lite,  are  commonly  associated  with  cinnabar.  A.  Liversidge  re- 
ports native  mercury  from  the  hot-spring  deposits  of  New  Zealand. 
According  to  J.  D.  Dana,  native  mercury  is  found  in  Venetian 
Lombardy  in  the  marl  beds  regarded  as  a  part  of  the  nummulitic 
beds  of  Eocene  age.  It  has  also  been  observed  in  the  drift  in 
Transylvania. 

Cinnabar  appears  to  have  more  than  one  method  of  forma- 
tion. According  to  F.  W.  Clarke,  mercury  and  sulphur,  under 
the  influence  of  heat,  unite  directly,  and  the  product  upon  sub- 
liming is  of  scarlet  hue.  The  black  sulphide  when  acted  upon 
by  solutions  of  alkaline  sulphides  can  be  converted  into  the  red 
form.  The  solubility  of  mercuric  sulphide  manifestly  depends 
upon  conditions  of  temperature,  pressure,  concentration,  and 
the  nature  of  the  solution  employed.  G.  F.  Becker  has  found 
that  mercuric  sulphide  is  precipitated  again  from  solution  in 
alkaline  sulphides  upon  dilution.  Relief  of  pressure  may  in 
some  cases  be  the  equivalent  of  dilution  as  a  precipitant.  A. 
Liversidge  has  reported  mercuric  sulphide  in  the  hot-spring 
deposits  of  New  Zealand.  Cinnabar  has  also  been  observed  in 
the  process  of  deposition  by  solfataric  action  at  Sulphur  Bank, 
California  and  Steamboat  Springs,  Nevada.  The  black  sulphide 
is  precipitated  whenever  H2S  meets  neutral  or  slightly  acid 
solutions  of  mercury  salts  in  the  mercuric  state.  It  does  not 
follow  that  the  mercurial  solutions  have  been  the  same  in  all 
localities.  They  must  have  varied  both  in  their  chemical  com- 
position and  in  the  physical  condition  under  which  they  canie 
to  the  surface.  Their  properties  would  be  modified  by  the  dif- 
ferences in  the  rocks  traversed  by  the  solutions  themselves. 

Calomel  is  a  product  of  secondary  origin  in  Idria  in  Carniola, 
Almaden  in  Spain,  Horzowitz  in  Bohemia,  Belgrade  in  Servia. 
Amalgam  is  often  formed  where  veins  of  mercury  and  silver 
intersect  each  other. 

Character  of  the  Ore  Bodies. — The  ore  bodies  bearing  mercury 
in  some  cases  fill  fissures,  fractures,  or  cavities  in  sedimentary  rocks. 
In  some  instances  cinnabar  forms  impregnation  deposits  in  sand- 
stones or  limestones.  These  terranes  are  usually  in  the  vicinity 
of  igneous  rocks  from  which  the  mercurial  ores  were  originally 
derived.  Deep-seated  granites  may  have  been  the  principal 


128  ECONOMIC  GEOLOGY 

source  of  the  mercury.  The  ores  of  mercury  occur  in  regions 
of  crustal  movement  and  are  newer  than  the  disturbed  rocks. 
They  are  not  confined  to  any  particular  formation,  nor  to  any 
type  of  rock. 

.Geographical  Distribution. — Mercury  has  a  wide  geographical 
range  but  its  occurrence  is  often  in  so  small  a  quantity  that  only 
a  few  localities  have  become  actual  producers.  California  has 
been  the  only  large  mercury  producer  in  the  United  States.  It 
occurs  in  many  western  states,  New  Mexico,  Nevada,  Oregon, 
Texas  and  Utah. 

According  to  H.  Ries,  the  California  ores  occur  chiefly  in  meta- 
morphosed Cretaceous  or  Jurassic  rocks,  and  some  even  are 
as  late  as  the  Miocene  and  Quarternary.  The  deposits  are  in 
fissured  zones.  Eruptive  rocks  seem  in  many  cases  to  be  in- 
volved in  the  ore  formation.  At  the  New  Almaden  mine  a 
rhyolite  dike  extends  parallel  with  the  ore  body.  The  ore  oc- 
curs along  the  contact  between  serpentine  and  shale,  filling  in 
part  the  interstices  of  a  breccia.  Branch  fissures  have  ore-bear- 
ing channels  extending  into  the  country  rock.  The  chief  gangue 
minerals  are  quartz,  calcite  and  dolomite.  The  ore  is  cinnabar 
with  a  little  native  mercury.  The  new  Almaden  mine  has  been 
one  of  the  most  important  mercury  deposits  of  the  world.  It 
has  been  worked  to  a  depth  of  nearly  3000  ft.  and  the  deposits 
are  diminishing  in  their  mercurial  content.  This  locality  is 
named  from  Almaden,  Spain,  where  the  metal  has  been  obtained 
for  years  in  great  abundance. 

The  New  Idria  mine,  named  from  Idria  in  Carniola,  has  been 
worked  almost  continuously  since  1853.  The  ore  occurs  in  the 
metamorphic  shales  and  limestones  of  Lower  Cretaceous  age. 
The  ore  is  irregularly  distributed  between  a  false  hanging  wall  of 
clay  and  a  foot  wall  of  shale.  The  ore  is  cinnabar-bearing  pyrite, 
with  a  gangue  of  silicified  and  brecciated  shales  and  sandstones. 
It  also  occurs  as  impregnation  deposits  and  in  reticulated  masses. 
Below  the  zone  of  oxidation  the  ore  body  contains  tabular  masses 
of  cinnabar.  Other  deposits  occur  at  Clear  Lake,  Sulphur  Bank, 
and  the  Great  Western  mine.  At  the  Great  Western  mine  the 
ore  occurs  as  chimney  deposits  in  opalized  quartz.  At  Steam- 
boat Springs,  Nevada,  cinnabar  is  intimately  associated  with 
hot  springs  and  occurs  as  impregnation  deposits  in  decomposed 
granite.  In  Texas  cinnabar  occurs  in  Cretaceous  limestone 
often  faulted,  in  fissure  veins  with  a  gangue  of  calcite. 


USEFUL  METALS  129 

The  most  important  deposits  of  mercurial  ores  in  the  world 
are  situated  in  southern  Spain  at  Almaden.  The  terranes  con- 
sist of  highly  tilted  and  metamorphosed  quartzites  and  shales  of 
Devonian  and  Silurian  age.  The  ore  bodies  occur  in  the  quartz- 
ite  as  impregnation  deposits,  or  as  stringers  running  through 
the  quartzite  beds.  The  impregnations  die  out  suddenly  where 
the  quartzites  are  in  contact  with  the  shales.  The  ore  is  cinnabar 
with  some  native  mercury,  pyrite  and  chalcopyrite. 

Another  important  mine  is  situated  at  Idria  in  Carniola, 
Austria.  It  occurs  in  limestones,  sandstones,  shales,  marls, 
dolomites,  and  conglomerates.  The  ore  body  is  an  impregna- 
tion deposit  in  the  limestones  and  dolomitic  breccias.  The 
ore  is  cinnabar  with  a  little  native  mercury.  The  gangue  min- 
erals are  quartz,  calcite,  dolomite  and  fluorite.  The  richest 
deposits  occupy  fissures. 

Geological  Horizon. — The  ores  of  mercury  are  not  confined 
to  the  rocks  of  any  particular  age.  The  Almaden  mine  in  Spain 
is  in  Silurian  and  Devonian  terranes.  The  New  Almaden  in 
California  is  in  the  Cretaceous.  The  Peru  terranes  bearing 
mercurial  ores  are  Jurassic. 

Methods  of  Extraction.  (1)  Distillation. — The  globules  of 
elemental  mercury  as  obtained  from  its  associated  gangue  min- 
erals or  in  pockets  in  the  vein  are  contaminated  with  certain 
impurities  that  may  be  left  in  the  retort  upon  distillation. 
The  metal  distills  at  a  temperature  of  350°  as  free  from  other 
metals.  In  this  process  the  metal  must  be  kept  free  from  oil 
or  oily  surfaces  for  these  " deaden"  the  mercury.  This  proc- 
ess is  utilized  in  the  recovery  of  mercury  from  the  amalgams 
of  gold  and  silver  obtained  in  the  reduction  of  the  precious 
metals. 

(2)  Roasting. — The  ores  of  mercury  are  crushed  and  roasted 
in  large  furnaces  of  from  40  to  50  tons  capacity  per  day  until 
the  last  traces  of  the  metal  are  driven  off.     The  temperature 
used  is  a  bright  red  heat.     This  high  temperature  is  needed  in 
order  to  warm  the  furnace  air  and  the  new  feeds  of  ore.     In 
this  process  the  sulphur  is  oxidized  to  sulphur  dioxide,  which 
when    conducted   into   water   forms   sulphurous   acid   used   so 
largely  in  the  manufacture  of  paper  by  the  sulphite  process. 

(3)  Sublimation. — As  calomel  volatilizes  without  suffering  de- 
composition it  is  only  necessary  to  crush  the  rock  bearing  this 
secondary  mineral  and  drive  off  the  chloride  of  mercury  as  a 


130  ECONOMIC  GEOLOGY 

vapor  by  heat.  The  calomel  condenses  in  the  cooling  chambers 
as  a  white  sublimate. 

Uses  of  Mercury. — The  most  important  use  of  mercury  is  to 
form  amalgams.  Most  metals  amalgamate  with  mercury. 
Sodium  and  potassium  amalgams  are  used  in  organic  analysis. 
Tin  amalgams  are  used  in  ordinary  mirrors,  gold  and  silver 
amalgams  in  filling  teeth.  A  common  amalgam  for  this  purpose 
consists  of  silver,  copper  and  tin  with  enough  mercury  to  amal- 
gamate the  mixture.  Copper  and  zinc  likewise  amalgamate 
with  mercury.  The  largest  single  use  lies  in  the  extraction  of 
the  precious  metals  from  their  various  ores.  Mercury  is  used 
in  thermometers  but  these  are  not  accurate  at  temperatures 
exceeding  30°  below  zero.  Mercury  is  used  also  in  the  arts,  as 
in  the  electrolytic  process  for  the  manufacture  of  sodium  and 
chlorine.  The  metal  is  unattacked  by  a  large  number  of  gases, 
therefore  it  is  used  in  collecting  and  measuring  gases  which  are 
soluble  in  water.  Mercury  compounds  are  used  in  medicine 
of  which  calomel  is  the  most  important.  The  bichloride  of 
mercury,  known  as  corrosive  sublimate,  is  used  in  mercurial 
ointment  and  as  an  antiseptic  for  dog  bites  and  snake  stings. 
The  sulphide  is  used  as  a  pigment  under  the  name  of  vermilion. 

The  unit  of  measure  for  mercury  is  different  from  that  of  the 
other  useful  metals.  The  liquid  metal  is  put  up  in  flasks.  Each 
flask  contains  75  Ib.  The  value  of  the  metal  is  determined 
by  the  market  at  San  Francisco.  An  average  quotation  is  about 
$45  per  flask.  The  output  of  mercury  in  the  United  States  in 
1910  was  1,612,500  Ib. 

There  are  two  conditions  that  oppose  a  large  production  of 
the  metal.  One  is  that  many  of  the  cinnabar  deposits  are 
situated  far  from  transportation  and  fuel.  The  other  is  that 
small  capital  is  not  likely  to  be  attracted  to  such  localities. 


CHAPTER  V 
USEFUL  METALS  CONTINUED  (GROUP  II,  SUBGROUP  A) 

BISMUTH,  COPPER  AND  CADMIUM 
Bismuth:  Its  Properties,  Occurrence  and  Uses 

Properties  of  Bismuth. — Bismuth,  symbol  Bi,  is  a  silvery 
white  metal  with  a  reddish  tinge.  Unlike  the  other  metals, 
save  antimony,  it  is  extremely  brittle.  It  is  unoxidized  at  the 
ordinary  temperature  in  dry  air  while  it  is  slowly  oxidized  in 
moist  atmosphere.  The  reddish  tinge  on  the  exposed  surfaces 
of  the  metal  is  the  result  of  such  oxidation.  It  expands  2  per 
cent,  upon  cooling  and  this  property  is  responsible  for  its  exten- 
sive use  in  the  manufacture  of  safety  plugs  for  boilers.  Chem- 
ically it  is  closely  allied  to  arsenic  and  antimony.  It  is  soluble  in 
HC1;  specific  gravity,  9.8,  melting  point,  269°  atomic  weight, 
208,  and  crystallizes  in  the  hexagonal  system. 

Ores  of  Bismuth. — Native  bismuth,  Bi,  100  per  cent.  It  is 
often  associated  with  gold,  silver,  and  several  of  the  useful 
metals. 

Bismuthinite,  Bi2S3,  81.2  per  cent,  bismuth. 

Guanajuatite,  Bi2Se3,  63.7  per  cent,  bismuth. 

Tetradymite,  Bi2Te3,  51.9  per  cent,  bismuth  when  sulphur 
free. 

Bismutite,  Bi203,H2C03,  80.6  per  cent,  bismuth.  A  basic 
carbonate  of  doubtful  composition. 

Bismutosphaerite,  Bi203,Bi2(C03) 3. 

Bismite,  Bi20s,  96.6  per  cent,  bismuth. 

There  are  also  arsenates  of  bismuth,  a  tellurate,  a  vanadate, 
a  silicate  and  an  oxychloride  of  the  same  base,  but  these  are 
rare  minerals.  The  native  metal  and  the  sulphide,  bismuth- 
inite,  are  the  most  widely  distributed  of  the  bismuth  minerals 
and  therefore  the  most  important  ores. 

Origin  of  the  Ores. — Native  bismuth  results  from  the  reduction 
of  other  ores  of  the  metal.  The  important  deposits  of  bismuth 
in  Bolivia  may  be  primary.  The  bismuth  is  intergrown  with 

131 


132  ECONOMIC  GEOLOGY 

cassiterite,  and  wolframite  may  sometimes  be  present.  The  sul- 
phide of  bismuth  is  sparingly  soluble  in  the  alkaline  sulphides 
and  in  that  way  may  be  transported  some  distance  from  the 
original  ore  body.  The  artificial  sulphide  is  precipitated  in  the 
chemical  laboratory  whenever  hydrogen  sulphide  comes  in  con- 
tact with  a  neutral  or  slightly  acid  solution  of  the  metal.  Ac- 
cording to  F.  W.  Clarke,  the  precipitated  sulphide  of  bismuth 
heated  with  an  alkaline  sulphide  at  a  temperature  of  200°  has 
given  crystals  of  bismuthinite.  The  carbonates  of  bismuth  are 
of  secondary  origin.  The  action  of  carbonated  waters  upon 
other  bismuth  minerals  has  produced  bismutite.  In  Aus- 
tralia bismutite  has  been  observed  as  an  ocherous  deposit  around 
a  thermal  spring.  Bismite  is  also  secondary  in  origin,  the  oxida- 
tion product  of  bismuthinite.  According  to  Mayengon,  bis- 
muthinite occurs  as  a  product  of  sublimation  from  burning  coal 
mines. 

Character  of  the  Ore  Bodies. — There  appears  to  be  no  well- 
marked  group  of  bismuth  veins.  The  bismuth  ores  are  best  re- 
garded as  subordinate  constituents  of  other  mineral-bearing  veins, 
yet  occurring  occasionally  in  such  commercial  quantities  as  to 
establish  exceptional  modifications  of  those  veins.  Veins  of 
bismuth  minerals  occur  in  gneiss  and  other  crystalline  rocks, 
also  in  clay  slate,  accompanying  various  ores  of  silver,  cobalt, 
lead  and  zinc.  In  Queensland  auriferous  bismuth  ores  are  con- 
nected with  granite  intrusives.  In  New  South  Wales  auriferous 
bismuth  veins  occur  near  the  contact  of  granite  and  slate.  In 
Bolivia  the  tin-bismuth  veins  appear  to  be  connected  with  dikes 
of  dacite  and  trachyte  traversing  altered  clay  slates. 

Geographical  Distribution. — The  best  known  locality  for  bis- 
muth minerals  in  the  United  States  is  in  Colorado.  Lake 
County  is  the  best  producer  of  the  brittle  metal.  According  to 
H.  Ries,  some  of  the  gold  ores  on  Breece  Hill  near  Leadville 
contain  from  5  to  8  per  cent,  of  bismuth.  In  the  same  state 
near  Golden  at  Bismuth  Queen  Lode  bismuth  ores  are  encoun- 
tered. It  is  found  also  at  Beaver  City,  Utah,  and  near  Tucson, 
Arizona.  In  fact,  the  Cordi Reran  section  bears  many  scattered 
occurrences  of  bismuth  ores.  Bolivia,  Germany  and  Austria  are 
the  large  producers  of  the  metal. 

Geological  Horizon. — The  ores  of  bismuth  do  not  appear  to 
be  confined  to  any  geological  horizon,  but  are  more  abundant 
in  the  older  geological  formations. 


USEFUL  METALS  133 

Methods  of  Extraction.  —  Bismuth  is  obtained  in  large  quan- 
tities as  a  by-product  in  the  treatment  of  gold,  silver  and  lead 
ores.  Two  methods  that  are  applicable  to  the  treatment  of 
bismuth  ores  may  be  outlined  as  follows: 

(1)  Roasting.  —  The  ore  is  crushed,  and  then  heated  in  re- 
torts. The  molten  metal  drains  off  through  inclined  iron  pipes. 
The  crude  metal  thus  collected  is  dissolved  in  nitric  acid,  form- 
ing the  nitrate  of  bismuth,  Bi(N03)3.  This  product  is  treated 
with  water  and  the  subnitrate  of  bismuth  is  formed  according 
to  the  equation, 


Bi(NO3)3+2H20  =  BiO,  N03,H20,+2HN03. 

After  the  precipitate  has  thoroughly  settled  the  supernatant 
liquor  is  drawn  off,  the  precipitate  dried,  and  the  oxide,  Bi2O3, 
is  formed.  This  oxide  when  roasted  in  large  crucibles  yields 
elemental  bismuth  and  carbon  monoxide  according  to  the  equa- 
tion, Bi203+3C  =  2Bi+3CO. 

(2)  Chlorination.  —  The  bismuth  ore  is  crushed,  pulverized,  and 
placed  in  a  series  of  wooden  vats  and  leached  with  chlorine 
solutions.  The  disengaged  chlorine  dissolves  the  bismuth. 
The  resulting  solution  is  clarified  by  filtering.  It  is  then  con- 
ducted into  water  when  the  bismuth  oxy  chloride,  BiOCl,  is 
formed.  The  bismuth  oxychloride  thus  precipitated  may  be 
dried  and  sold  directly  or  it  may  be  roasted  with  lime  when 
chloride  of  lime  and  elemental  bismuth  are  obtained.  There 
are  several  other  processes  for  the  manufacture  of  metallic 
bismuth  in  foreign  countries  but  owing  to  the  minor  importance 
of  the  metal  they  are  omitted. 

Uses  of  Bismuth.  —  Bismuth  is  used  in  the  treatment  of  the 
precious  metals  for,  like  lead,  it  acts  as  a  collecting  agent  for 
these  metals.  Its  recovery  power  is  very  high  for  both  gold 
and  silver.  The  most  important  use  of  bismuth  is  in  the  manu- 
facture of  many  alloys  which  are  capable  of  wide  industrial 
application.  Perhaps  the  most  important  of  these  is  Wood's 
fusible  metal  which  melts  at  65°.  The  alloy  consists  of  4  parts 
of  bismuth,  2  parts  of  lead,  1  part  of  tin  and  1  part  of  cadmium. 
The  melting-point  is  far  lower  than  that  of  any  of  its  constituents. 
Bismuth  melts  at  269°,  lead  at  327°,  tin  at  232°,  and  cadmium 
at  321.7°  C.  Other  alloys  are  Lippowitz'  metal,  fusing  at  60°; 
Dorocot's  metal,  fusing  at  93°;  Newton's  fusible  metal,  fusing  at 


134  ECONOMIC  GEOLOGY 

94.5°;  Rose's  metal,  fusing  at  about  100°.  The  range  of  the 
melting  point  of  these  alloys  between  60°  and  100°  renders  them 
capable  of  industrial  application,  as  on  passenger  and  freight 
trains  where  gas  is  used  for  lighting  and  as  safety  fuses  for  elec- 
trical apparatus.  Britannia  metal  is  an  alloy  which  carries  1.8 
per  cent,  of  bismuth.  One  variety  of  type  metal  carries  7.6,  per 
cent,  of  bismuth.  With  zinc  the  alloys  of  bismuth  are  always 
of  definite  composition. 

The  alloys  of  bismuth  expand  upon  cooling,  therefore  they 
make  fine,  hard,  sharp  castings  and  are  used  for  safety  plugs 
to  fill  blow  holes  in  boilers.  These  alloys  are  used  also  in  the 
production  of  wood  cuts.  Some  of  the  alloys  known  as  bis- 
muth solders  have  so  low  a  melting  point  that  they  can  be  used 
directly  under  hot  water.  Bismuth  is  used  also  in  the  manu- 
facture of  clique  metals.  It  is  utilized  in  the  preparation  of 
glass  of  high  refractive  power.  Bismuth  unites  with  mercury 
in  the  formation  of  dental  amalgams.  Bismuth  is  used  quite 
extensively  in  medicine,  the  subnitrate  being  the  most  important 
compound.  It  is  used  in  cosmetics,  in  calico  printing  and  several 
of  its  salts  in  the  chemical  trade.  Bismuth  is  one  of  the 
most  objectionable  constituents  in  brass. 

The  world's  supply  of  bismuth  has  long  been  controlled  by 
Johnson,  Mathey  &  Co.  of  England,  who  have  regulated  abso- 
lutely the  production  of  bismuth,  the  price  of  the  metal,  and  the 
supply  of  its  ores.  An  attempt  has  been  made  to  establish  a 
price  that  would  be  renumerative  to  both  the  mine  owners  and 
the  producers.  The  price  of  bismuth  ores  in  London  depends 
upon  the  bismuth  content.  With  the  metal  at  $1.25  per  pound 
the  following  values  would  be  attached  to  the  ores:  10  per  cent. 
ore  would  be  worth  $150  per  ton;  15  per  cent.,  $200;  20  per  cent., 
$350;  30  per  cent.,  $550;  35  per  cent.,  $650;  40  per  cent.,  $750; 
45  per  cent.,  $850;  50  per  cent.,  $1000. 

The  small  amount  of  bismuth  ore  produced  in  the  United 
States  was  formerly  sent  abroad  for  reduction.  Plants  have 
recently  been  established  at  St.  Louis,  Missouri  and  Grasselli, 
Indiana,  for  the  recovery  of  bismuth  from  lead  ores.  Bismuth,  as 
already  noted,  is  contained  in  other  ores  than  lead,  but  most  of 
the  bismuth  passes  into  the  atmosphere  through  the  smelter 
flues  unrecovered.  It  is  estimated  that  880  Ib.  of  bismuth  are 
thrown  off  in  every  24  hours  in  the  smoke  and  gases  of  the 
Washoe  smelter. 


USEFUL  METALS  135 

Copper :  Its  Properties,  Occurence  and  Uses 

Properties  of  Copper. — Copper,  symbol  Cu,  is  a  copper  red  to  red- 
dish-brown, soft,  ductile  and  malleable  metal.  Its  color  as  copper 
red  is  best  seen  by  reflected  light.  It  is  extremely  tough,  there- 
fore, capable  of  being  drawn  out  into  exceedingly  fine  wires  or 
hammered  out  into  thin  leaves.  Its  ductility  and  malleability 
are  greatly  diminished  by  the  presence  of  impurities.  As  an 
electrical  conductor  it  is  second  only  to  silver.  The  metal  slowly 
tarnishes  in  dry  air  but  in  a  moist  atmosphere  it  is  readily  coated 
with  a  basic  green  carbonate.  It  is  readily  soluble  in  the  mineral 
acids.  Its  specific  gravity  is  8.9.  It  melting  point  is  1065. 
Its  atomic  weight  63.57. 

Ores  of  Copper. — Native  copper,  Cu,  100  per  cent,  copper  but 
often  alloyed  with  gold,  silver,  lead  and  mercury. 

Chalcocite,  Cu2S,  79.8  per  cent,  copper.     A  gray  sulphide. 

Covellite,  CuS,  66.4  per  cent,  copper.     An  indigo  blue  sulphide. 

Bornite,  Cu2S,CuS,FeS,  55.5  per  cent,  copper.  Known  as 
horseflesh  ore  by  miners. 

Chalcopyrite,  CuFeS3,  34.5  per  cent,  copper.  The  most  im- 
portant source  of  the  metal. 

Tetrahedrite,  4Cu2S,Sb2S3,  30.4  per  cent,  copper.  Often 
argentiferous. 

Tennantite,  4Cu2S,As2S3,  57.5  per  cent,  copper. 

Enargite,  3Cu2S,As2S5,  48.3  per  cent,  copper. 

Chalcanthite,  CuSo4,5H2O,  25.4  per  cent,  copper.  A  natural 
blue  vitriol. 

Brochantite,  CuS04,(3CuOH)2,  62.4  per  cent,  copper. 

Cuprite,  Cu20,  88.8  per  cent,  copper.     The  red  oxide  of  copper. 

Tenorite,  CuO,  79.8  per  cent,  copper.  The  black  oxide  of 
copper. 

Malachite,  CuC02,Cu(OH)2,  57.4  per  cent,  copper.  The  green 
carbonate. 

Azurite,  2CuC03,Cu(OH)2,  55  per  cent,  copper.  The  blue 
carbonate. 

Nantokite,  Cu2Cl2,  64.1  per  cent,  copper. 

Atacamite,  CuCl2,Cu(OH)2,  59.4  per  cent,  copper. 

Dioptase,  CuSi03,H20. 

Chrysocolla,  CuSi03,2H2O. 

Origin  of  the  Ores. — Copper  is  widely  distributed  in  nature. 
The  metal  is  easily  oxidizable  and  also  easily  reduced.  It  there- 


136  ECONOMIC  GEOLOGY 

fore  occurs  both  as  native  copper  and  in  its  numerous  compounds. 
Copper  is  found  in  small  quantities  in  the  igneous  rocks  and  there- 
fore in  the  sedimentaries  derived  from  them.  It  is  a  common 
constituent  of  sea  water,  and  the  green  color  of  the  sea  has  been 
attributed  to  its  presence.  Copper  has  been  obtained  in  the 
ashes  of  sea  weeds  and  found  in  certain  varieties  of  corals. 

According  to  F.  W.  Clarke,  native  copper  is  commonly,  if  not 
always,  of  secondary  origin,  either  deposited  from  solution  or 
formed  by  the  reduction  of  some  solid  compound.  Pseudo- 
morphs  of  copper  after  cuprite  are  well  known.  W.  S.  Yeats  has 
described  pseudomorphs  of  copper  after  azurite  from  Grant 
County,  New  Mexico.  W.  Lindgren  states  that  the  vein  of 
metallic  copper  at  Clifton,  Arizona,  appear  to  have  been  derived 
from  Chalcocite.  T.  Carnely  has  shown  that  native  copper  is 
soluble  in  saline  water.  Small  quantities  of  native  copper  have 
been  found  at  both  the  Ely  mine  in  Vershire,  Vermont,  and  in  the 
Corinth  mine  in  Cornith,  Vermont,  that  appear  to  have  been 
formed  from  very  dilute  sulphate  solutions.  The  greatest  known 
deposits  of  metallic  copper  are  found  in  the  Lake  Superior  region. 
F.  W.  Clarke  states  its  original  home  was,  perhaps  as  sulphide, 
in  the  unaltered  igneous  rocks,  but  its  concentrates  are  now  found 
in  the  sandstones,  conglomerates,  and  amygdaloids.  In  the 
sandstones  and  conglomerates  it  acts  as  a  cement.  It 'also  re- 
places pebbles  and  even  boulders  a  foot  or  more  in  diameter.  A. 
C.  Lane  has  cited  a  corroded  quartz  crystal  which  was  mainly 
replaced  by  copper.  Frequently  native  copper  has  been  reported 
as  holding  enclosed  nodules  of  native  silver.  According  to  F.  W. 
Clarke,  if  these  metals  had  been  deposited  from  a  fused  magma 
they  should  not  have  solidified  separately,  but  as  an  alloy. 

R.  Beck  mentions  native  copper  filling  the  marrow  cavities  of 
fossil  bones  in  the  Peruvian  sandstones  of  Corocoro,  Bolivia. 
E.  Haworth  cites  films  of  copper  in  the  shales  near  Enid, 
Oklahoma,  which  were  precipitated  by  organic  substances. 

The  largest  single  mass  of  native  copper  ever  found  was  dis- 
covered in  the  Minnesota  mine,  Michigan,  in  February,  1857. 
It  was  45  ft.  long,  22  ft.  wide  and  8  ft.  thick.  It  weighed  420 
tons.  It  was  90  per  cent,  pure  copper  and  contained  an  appre- 
ciable amount  of  silver.  The  value  of  that  single  specimen  at 
the  average  price  of  copper  would  be  about  $83,000. 

Chalcopyrite  is  the  most  important  ore  of  copper.  Bornite 
and  chalcocite  are  next  in  importance  at  least  among  the  sulphides. 


USEFUL  METALS  137 

These  three  minerals  have  been  repeatedly  indentified  as  of  mag- 
matic  differentiation.  They  are  doubtless  the  primary  com- 
pounds from  which  the  other  ores  in  most  cases  were  derived. 
B.  Lotti  has  reported  chalcopyrite,  bornite  and  chalcocite  in 
Tuscany  as  original  segregations  in  serpentinized  rocks.  J.  F. 
Kemp  has  reported  primary  bornite  in  a  pegmatite  vein  near 
Princeton,  British  Columbia.  The  various  sulphides  of  copper 
are  often  of  hydatogenetic  origin.  Sulphides  of  more  electro- 
positive metals  may  have  served  as  precipitating  reagents.  Cu- 
pric  solutions  formed  in  the  upper  part  of  copper- bearing  ore 
bodies  reacting  upon  pyrite  precipitate  chalcocite.  Covellite  may 
be  precipitated  from  copper  sulphate  solutions  by  the  reaction  of 
chalcocite.  Chalcocite  may  alter  into  chalcopyrite  and  bornite. 

According  to  Thomas  and  MacAlister  chalcopyrite  may  be  of 
metasomatic  origin.  The  mode  of  deposition  of  chalcopyrite 
in  a  certain  number  of  deposits  like  those  formed  in  limestone  or 
at  its  contact  with  other  rocks  leads  to  this  conclusion.  The  same 
authors  state  that  the  solutions  may  have  come  from  above  or 
below.  The  solutions  were  transported  in  the  form  of  sulphates, 
either  due  to  the  oxidation  of  pyrite  in  the  neighboring  rocks,  or 
in  the  form  of  aqueous  emanations  from  an  igneous  magma  dur- 
ing the  later  stages  of  its  cooling.  They  also  state  that  the 
metasomatic  chalcopyrite  deposits  are  due  to  ascending  or  de- 
scending solutions  of  sulphides  carrying  hydrogen  sulphide  and 
alkaline  sulphides. 

The  sulphates  of  copper  are  formed  by  the  oxidation  of  the 
surface  ores  of  copper  and  iron  and  the  concentration  of  the  mine 
waters.  At  Wicklow,  Ireland,  and  Rio  Tinto,  Spain,  chalcan- 
thite  thus  formed  has  been  a  workable  deposit.  According  to 
H.  Ochmichen,  chalcanthite  occurs  in  Chili  as  an  impregnation 
deposit  in  partially  decomposed  granite  rocks  with  the  hydrous 
carbonates  and  silicates  as  associated  minerals.  Brochantite  is 
far  more  common  than  is  usually  supposed  and  can  be  easily 
formed  by  natural  reaction. 

The  two  basic  carbonates  of  copper,  malachite  and  azurite, 
are  common  copper  ores  of  secondary  origin.  They  are  formed 
in  the  upper  portion  of  ore  bodies  by  the  action  of  carbonated 
waters  upon  copper  compounds  or  by  the  reactions  between 
cuprous  solutions  and  limestone.  At  Corinth,  Vermont,  the 
author  has  found  fine  specimens  of  both  malachite  and  azurite 
formed  from  chalcopyrite  by  the  action  of  carbonated  waters. 


138  ECONOMIC  GEOLOGY 

L.  Michel  has  reproduced  azurite  by  leaving  a  solution  of  copper 
nitrate  in  contact  with  a  crystal  of  calcite  for  several  years.  The 
carbonates  have  also  been  observed  in  the  patina  of  ancient 
bronzes. 

Nantokite,  the  cuprous  chloride,  is  rather  rare,  but  atacamite, 
especially  in  Chili,  is  important.  According  to  J.  D.  Dana,  it 
may  be  formed  by  the  oxidation  ofnantokite.  F.  W.  Clarke 
states,  that  it  has  been  observed  upon  ancient  coins  and  bronzes. 
The  fumes  of  HC1  acting  upon  tenorite  has  produced  a  hydrous 
chloride  that  is  not  far  from  atacamite  in  composition  and  cor- 
responds very  closely  to  the  hydrous  chloride  found  at  Mount 
Vesuvius  as  a  product  of  volcanic  emanation  during  the  eruption 
of  1872. 

The  two  oxides,  cuprite  and  tenorite,  are  always  of  secondary 
origin.  They  may  be  formed  by  the  oxidation  and  reduction 
of  other  copper  minerals.  Cuprite  is  far  the  more  important 
species.  It  has  been  observed  as  an  incrustation  upon  ancient 
objects  of  copper  or  bronze. 

Of  the  two  silicates  of  copper,  dioptase  and  chrysocolla,  the 
first  is  rare  but  the  second  becomes  an  important  copper  ore  in 
certain  localities.  According  to  F.  W.  Clarke,  chrysocolla  is 
formed  by  the  action  of  silica-bearing  waters  upon  soluble  com- 
pounds of  copper.  Also  that  the  mineral  may  possibly  be  pro- 
duced during  the  processes  of  secondary  enrichment. 

H.  Ries  gives  the  following  classification  of  the  origin  of  cop- 
per ores: 

(1)  Magmatic  segregations.     No  workable  deposits  of  mag- 
matic  origin  are  known  in  the  United  States. 

(2)  Contact   deposits  in   crystalline  limestone  along  contact 
with  igneous  rocks.     The  copper  has  been  introduced  by  vapors 
from  the  igneous  rocks. 

(3)  Deposits  formed  by  ascending  circulating  hot  solutions, 
depositing  ores  in  fissures,  pores,  spaces  of  brecciation,  and  by 
replacement  of  rock. 

(4)  Lens-shaped   deposits   in  crystalline  schists  representing 
a  concentration  of  material  from  a  disseminated   condition  in 
the  surrounding  rocks. 

The  last  two  are  by  far  the  most  important,  but  even  here  the 
ores  have  been  enriched  by  oxidation  and  the  transference  of 
soluble  compounds  of  copper  to  lower  levels  to  be  reprecipitated 
by  limestone  and  the  sulphides  of  copper  and  iron. 


USEFUL  METALS 


139 


Character  of  the  Ore  Bodies. — Primary  copper  sulphides  are 
found  at  Cornwall,  England,  in  veins  containing  cassiterite.  In 
Norway,  where  primary  sulphides  occur:  tin  is  absent  and  the  ores 
are  associated  with  greisen  and  derived  from  acid  irruptives 
during  their  solidification.  In  Telemarken  in  Southern  Norway 
copper  ores  occur  with  tourmaline  in  granites,  gneisses  and 
schistose  rocks.  At  the  Ely  mine  in  Vershire,  Vermont,  the 
chalcopyrite  is  associated  also  with  tourmaline.  The  ore  occurs 


FIG.  81. — Polished  specimen  of  copper  ore  from  Rambler  mine,  Wyom- 
ing. The  dark  mineral  in  corellite.  The  light  is  kaolinized  feldspar. 
(After  Mineral  Resources,  1902,  U.  S.  Geological  Survey.) 

in  saddle-shaped  bodies  along  the  folds  in  the  Vershire  schists 
or  in  long  chimneys  at  the  contact  of  the  intrusive  granite  with 
the  Vershire  schists.  Pyrite  and  pyrrhotite  are  the  common 
associated  sulphides.  The  granite  was  the  parent  home  of  the 
copper  and  the  chalcopyrite  was  deposited  under  pneumatolytic 
conditions.  This  mine  was  known  and  worked  before  copper 
was  discovered  in  the  Lake  Superior  region.  In  the  earlier  days 
with  16  per  cent,  copper  ore  the  mine  was  capable  of  pro- 


140  ECONOMIC  GEOLOGY 

ducing  10,000,000  Ib.  of  copper  per  annum,  but  in  the  later  years 
much  of  the  ore  has  not  exceeded  3  per  cent,  copper. 

According  to  Thomas  and  MacAlister,  sulphidic  copper  ores 
occur  in  South  Australia  in  veins  sometimes  30  ft.  in  width  and 
of  hydatogenetic  origin.  They  occur  in  the  mica  schists  of  Cam- 
brian age  and  the  associated  minerals  are  pyrite,  hematite  and 
molybdenite.  They  also  describe  in  New  South  Wales  the  exist- 
ence of  interbedded  veins  of  a  cupriferous  pyrrhotite  with 
chalcopyrite,  chalcocite  and  magnetite  present. 

Metasomatic  replacements  of  copper  ores  occur  at  Bisbee, 
Arizona,  and  in  the  Lake  Superior  region.  The  high  grade  cop- 
per ores  of  northern  Italy  are  considered  by  some  to  be  of  the  same 
origin  (Fig.  81). 

The  form  then  that  the  various  copper  deposits  assume  are 
veins,  contact  zones,  impregnations  and  replacements  in  sedimen- 
tary rocks. 

Geographical  Distribution. — The  copper  ores  of  the  United 
States  form  five  distinct  belts:  (1)  The  Appalachian  belt;  (2) 
the  Lake  Superior  region;  (3)  the  Cordilleran  section;  (4)  the 
Pacific  Coast  belt,  and  (5)  the  Alaskan  belt. 

(1)  The  Appalachian  Belt. — This  belt  extends  from  Alabama 
on  the  south  in  a  northeasterly  direction  to  Newfoundland  on 
the  north.  The  richest  deposits  occur  in  Tennessee,  Vermont 
and  Newfoundland.  The  largest  producing  mine  in  the  belt  is 
at  Ducktown,  Tennessee.  The  ore  occurs  as  true  fissure  veins 
in  the  crystalline  schists.  It  consists  chiefly  of  chalcopyrite  in 
pyrrhotite  and  pyrite  with  a  little  quartz  and  is  the  richest  where 
the  pyrrhotite  is  the  most  abundant.  According  to  H.  Hies  this 
district  was  one  of  the  earliest  producers  of  copper  in  the  United 
States.  The  operations  were  commenced  as  early  as  1850.  The 
ores  resulting  from  secondary  enrichment  were  soon  worked  out 
and  it  was  not  until  1890  that  the  underlying  low-grade  sulphides 
were  successfully  worked.  Since  that  time  the  mine  has  been  a 
steady  producer. 

At  Gold  Hill,  North  Carolina,  chalcopyrite  occurs  in  true 
fissure  veins  found  along  sheeted  planes  in  the  metamorphics. 
Pyrite  is  associated  with  the  copper  ore. 

At  Virgilina,  Virginia,  the  ore  is  bornite  with  a  little  chalcopy- 
rite and  pyrite.  It  occurs  in  true  fissure  veins  filled  with  quartz 
and  sulphides.  The  veins  conform  to  the  banding  of  the  mica 
schists.  Replacements  of  the  wall  rock  are  rare.  In  Green 


USEFUL  METALS  141 

County,  Virginia,  segregations  of  native  copper,  together  with 
the  oxides,  cuprite  and  tenorite,  and  the  carbonates,  malachite 
and  azurite,  occur  along  sheared  zones  in  the  altered  rocks  of 
Algonkian  age. 

In  Pennsylvania,  New  Jersey  and  Connecticut,  deposits  of 
native  copper  are  found  along  the  contact  of  diabase  and  the 
intruded  sandstones.  The  mines  in  these  states  have  never  been 
large  producers  (Fig.  82). 

The  four  copper  mines  worked  from  time  to  time  in  Vermont 
are  the  Ely  mine  in  Vershire;  the  Corinth  mine  in  Corinth; 
the  Elizabeth  mine  and  the  Strafford  mine  in  Strafford,  Vermont. 
These  are  all  in  Orange  County,  and  are  now  idle  owing  in  part 


FIG.  82. — Ely  mine,   Copperfield,  Vermont,  showing  the  large  slag  beds 
in  the  foreground.     (By  courtesy  of  the    Vermonter.) 

to  the  depletion  of  the  available  ore  bodies  and  in  part  to  the 
distance  from  railroad.  The  chief  ore  in  each  was  chalcopyrite 
associated  with  pyrrhotite  and  pyrite.  The  ore  is  in  saddle- 
shaped  bodies  in  the  Vershire  schists  and  in  chimneys  at  the 
contact  of  the  granite  with  the  Vershire  schists.  The  schists 
and  the  associated  limestones  are  of  Ordovician  age.  Tour- 
malines and  garnets  are  abundant  (Fig.  83). 

The  copper  ores  of  the  Appalachian  belt  are  somewhat  aurifer- 
ous. The  early  attempts  to  work  the  ores  for  both  the  gold 
and  the  copper  content  resulted  in  failure.  The  Vermont  ores 
averaged  about  $2  per  ton  in  gold.  The  Newfoundland  ores  are 
higher  in  their  gold  content.  Much  of  that  ore  assays  from  $2 


142 


ECONOMIC  GEOLOGY 


to  $6  in  gold.  Some  of  the  veins  on  the  eastern  coast  of  New- 
foundland are  true  fissure  veins  traversing  sandstones  and  con- 
glomerates. Intrusive  diabase  appears  to  be  the  home  of  the 
copper  ore.  Chalcopyrite  and  pyrite  are  the  chief  minerals. 

Chalcopyrite  occurs  in  considerable  quantity  at  Capleton, 
Province  of  Quebec,  in  a  sheared  amygdaloid.  The  mine  has 
been  a  steady  producer  for  a  number  of  years. 

(2)  The  Lake  Superior  Region. — This  region  was  discovered  by 
Douglas  Houghton  in  1830.  It  has  since  that  time  produced  more 
native  copper  than  all  other  localities  put  together.  In  fact  it 
has  become  one  of  the  most  famous  copper  producing  districts 
of  the  world.  The  rocks,  known  as  the  Keweenaw  series,  consist 


FIG.  83. — Dump  piles  of  the  Ely  mine,  Copperfield,  Vermont.     (By  courtesy 

of  the  Vermonter.) 

of  interbedded  lava  flows,  sandstones  and  conglomerates.  The 
conglomerates  consist  of  rounded  fragments  of  a  reddish  quartz 
porphyry  of  igneous  origin. 

The  ore  is  native  copper  occasionally  associated  with  native 
silver.  It  occurs,  according  to  H.  Hies:  (1)  As  a  cement  in 
the  conglomerate,  or  replacing  the  conglomerate;  (2)  as  a  filling  in 
the  amygdules  of  the  lava  beds;  and  (3)  as  masses  of  irregular 
and  often  large  size  in  veins  with  calcite  and  zeolitic  gangue.  (See 
Fig.  84.) 

According  to  A  C.  Lane,  the  original  lava  flows  was  the  home 
of  small  percentages  of  copper,  and  while  these  basaltic  rocks 
were  still  heated  they  absorbed  sea  waters  charged  with  sodium 


USEFUL  METALS 


143 


144  ECONOMIC  GEOLOGY 

chloride.  Meteoric  waters  transferred  the  sodium  chloride  down- 
ward and  in  their  downward  transition  they  dissolved  the  copper 
as  copper  chloride.  Reactions  between  the  original  minerals  of 
the  volcanics  and  the  copper  solution  gave  rise  to  native  copper, 
calcium  chloride  and  soduim  silicates. 

The  following  assemblage  of  facts  bearing  on  the  source  of  the 
copper  in  the  Lake  Superior  district  is  taken  directly  from  the 
masterly  work  of  A.  C.  Lane  on  the  Keweenaw  Series  of  Michigan. 

(A)  The  dissemination  of  copper  in  small  quantities  through- 
out the  formation.     The  average  from  several  thousand  feet  of 
drilling  at  the  Clark-Montreal  mine  was  0.02  per  cent.     Hardly 
a  single  amygdaloid  fails  to  carry  less  than  0.02  per  cent,  copper, 
and  when  the  copper  content  reaches  0.5  per  cent,  it  is  nearly 
an  ore. 

(B)  The  occurrence  of  native  copper  in  similar  formations  of  the 
red  rock  associated  with  salt  waters  and  lavas  elsewhere,  notably 
in  the  New  Jersey  Triassic,  in  the  Bolivian  Puca  sandstone,  in 
Nova  Scotia,  around  Oberstin,  in  the  Naho  melaphye  region,  and 
in  Alaska. 

(C)  The  general  absence  of  native  copper  outside  the  Keween- 
awan,  in  the  Lake  Superior  region,  but — 

(D)  Native  copper  has  been  found  in  iron  ore  (generally  thought 
to  be  formed  by  the  action  of  downward  working  waters)  in  a  few 
places. 

(E)  The  water  in  the  formation  is  of  three  kinds. 

(a)  At  and  near  the  surface  soft  and  fresh  with  sodium  in 
quantities  more  than  sufficient  to  combine  with  the  chlorine. 

(6)  At  some  distance  (generally  500  to  2000  ft.,  before  it  attracts 
attention,  unless  especially  sought)  the  chlorine  is  higher  and  the 
water  is  charged  with  common  salt.  The  line  between  the  two 
classes  of  waters  is  often  quite  sharp. 

(c)  At  greater  depths  a  strong  solution  of  calcium  chloride 
contains  some  copper. 

(F)  The  middle  water  b  often  contains  more  salt  than  it  could 
possibly  have  were  it  a  mixture  of  a  and  c. 

(G)  The  lines  between  the  different  kinds  of  waters  are  not 
regular,  yet  the  lowest  water  probably  always  comes  within  2000 
or  3000  ft.  of  the  surface. 

(H)  The  amygdaloids  seem,  other  things  being  equal,  to  contain 
rather  stronger  (more  saline)  water  than  the  conglomerates. 

(I)  An  unequally  heated  solution  corresponding  to  mine  water 


USEFUL  METALS  145 

c  will  precipitate  copper  on  the  same  minerals,  prehnite,  datolite, 
etc.,  on  which  it  occurs  in  the  mine,  as  Fernekes  has  shown. 

(J)  The  traps  contain  combustible  gases,  as  R.  T.  Chamberlain 
has  shown. 

(K)  Certain  beds  are  abnormally  rich  in  copper  for  many 
miles. 

(L)  Copper  often  replaces  chlorite,  and  in  the  Calumet  &  Hecla, 
pebbles  chlorite  replaces  felsite,  and  the  copper  the  chlorite. 

(M)  Copper  may  even  replace  vein  quartz. 

(N)  Copper  is  formed  generally  after  those  minerals  which  are 
the  products  of  alteration  and  contain  lime,  and  before  those  sec- 
ondary minerals  which  are  the  products  of  alteration  and  contain 
soda  and  potash. 

(0)  Therefore  at  the  time  the  copper  formed  the  mine  water 
might  have  lost  lime  but  could  not  have  lost  sodium.  The  rock 
might  have  lost  both. 

(P)  The  Calumet  &  Hecla  lode  averages  less  rich  (very  rich 
in  spots)  near  the  surface,  attains  its  greatest  richness  at  a  cer- 
tain depth,  say  about  2,000  ft.,  and  then  gradually  decreases  in 
richness. 

(Q)  The  silver  occurs  more  abundantly  in  the  upper  levels. 

In  producing  the  copper  solution  and  guiding  it  in  its  circula- 
tion Lane  considers  the  following  factors: 

(A)  The  waters  were  originally  contained  in  the  lava. 

(B)  That  which  early  filled  it,  whether  it  was  buried  on  land 
or  beneath  seas,  may  have  included  condensed  volcanic  vapors 
containing  copper  chloride,  as  in  Stromboli,  or  in  the  evaporation 
of  desert  pools. 

(C)  The  absorption  of  water  in  the  hydration  of  the  rocks. 

(D)  The  absorption  of  water  in  the  cooling  of  the  formation 
(water  in  cooling  shrinks  more  than  rock) . 

(E)  Faults  in  the  formation  facilitating  the  intermingling  of 
solutions  of  different  compositions. 

(F)  Erosion  of  the  formation  and  concentration  of  the  copper 
contained  either  in  pools  on  the  land  surface  or  in  the  water  which 
found  its  way  down  into  the  rocks,  while  the  deposition  of  the 
Keweenawan  as  a  land  formation  was  going  on. 

(G)  The  ordinary  circulation  of  the  water  entering  at  the 
higher  parts  and  emerging  in  springs. 

(3)  The  Cordilleran  Section. — (See  Fig.  85.)     Butte,  Montana, 

is  the  most  important  mining  camp  in  this  district.     In  fact  it  is 
10 


146 


ECONOMIC  GEOLOGY 


one  of  the  largest  producers  of  copper  in  the  world.     Its  output  has 
been  approximately  2,000,000,000  Ib.  of  copper.     It  has  further- 


p^^tsi 

r     •••••Mi 


•SILVER  VEINS 
COPPER  VEINS 


[•  i  ..;;;|  Pal  -  ALLUVIUM  AND  WASH  PLEISTOCENE  

|jf«;»3    Nrl  -  INTRUSIVE  RHYOLITE  NEOCENE 

Eliil    ap-    APLITE      ) 

>-  POST  CARBONIFEROUS 

fcyv)  qr-  GRANITE  J 

FIG.  85. — Map  of  the  eastern  part  of  Butte,  Montana,  district,  showing 
distribution  of  Veins  and  geology.  (By  permission  of  the  Macmillan 
Company,  from  Ries1  Economic  Geology.) 

more  produced  more  than  100,000,000  oz.  of  silver  and  500,000 
of  gold.  The  camp  began  its  mining  career  as  a  gold  producer 
in  1864.  It  held  this  recognition  until  1875  when  it  became  a 


USEFUL  METALS 


147 


silver  camp.  It  maintained  this  position  until  about  1880  when 
it  became  a  copper  camp.  It  will  always  remain  in  the  literature 
of  mining  geology  as  distinctively  a  copper  camp  (Fig  86) . 

The  primary  ore  was  chalcopyrite  and  pyrite.  It  is  the  enor- 
mous deposits  of  secondary  chalcocite  that  have  been  the  large 
producers  of  the  metal.  Other  copper  minerals  appearing  as  ores 
are  bornite,  enargite,  covellite  and  tetrahedrite.  The  veins  are 


FIG.  86. — Geologic  map  of  the  western  half  of  Butte,  Montana,  district. 
(B.y  permission  of  the  Macmillan  Company,  from  Ries1  Economic  Geology.} 


quite  largely  replacement  deposits  along  fissures  in  the  sheeted 
granite.  The  country  rock  consists  of  two  types  of  granite.  One 
is  a  dark  hornblendic  granite  or  quartz  monzonite  known  as  the 
Butte  granite.  The  other  is  an  acid  granite  or  better  an  aplite 
termed  the  Bluebird  granite.  These  granites  are  intersected 
by  dikes  of  quartz  porphyry.  Dikes  of  both  intrusive  and  extru- 
sive rhyolite  intersect  the  copper  veins. 


148 


ECONOMIC  GEOLOGY 


According  to  H.  Hies,  the  veins  exhibit  a  curious  uniformity 
of  direction,  most  of  them  striking  nearly  east  and  west,  and  few 
of  them  departing  more  than  15  or  20  degrees  from  the  vertical. 


I  -3 


3    £ 

O     £ 


4 


r^    02 

w  § 
.  a 


a 

T 


They  show  considerable  variation  in  width,  ranging  from  a  few 
feet  to  150  ft.  where  the  altered  country  rock  is  impregnated  with 
chalcocite.  In  some  instances  there  is  no  distinct  hanging  wall 


USEFUL  METALS 


149 


and  the  distinction  between  the  vein  and  the  country  rock  be- 
comes commercial. 

The  surface  material  consists  of  a  red  or  brown  quartz.     Beneath 


CSJ 


fl  o 

O    ?S5 

N      <to 

<   I 
-05 

II 
(§1 

" 


'Bed 


this  there  is  a  zone  of  oxides  carrying  both  gold  and  silver.  The 
alteration  products  at  times  reach  a  depth  of  300  ft.  or  more,  de- 
pending upon  the  susceptibility  of  the  original  material  to  the 


150 


ECONOMIC  GEOLOGY 


agencies  of  the  weather  and  meteoric  water.  Beneath  this  there 
is  a  zone  of  unaltered  sulphides  which  furnish  the  main  ores  of  the 
camp. 

According  to  W.  H.  Weed,  hot  alkaline  solutions  leached  the 
metals  from  the  granite  at  considerable  depths  and  wherever  the 
fissures  were  open  they  were  filled  with  ore  and  where  the  fissures 


Bad  nodnlar  shales  with 
bedded,  buff.  uwm.  and  red 
few  beds  of  iin- 
base.  Un- 
comfortably overlain  by  fluviu- 
tile  Quaternary  deposits. 


3intura  formation,  1, 
plus  unknown   thickness, 
removed  by  erosion. 


Uck.UdlM.  na,d.  gray,  foasil- 
fossll- 


BurT,  tawny  and  re3  sandstones 
and  dark-red  shales,  with  an 
occasional  thin  bed  of  impure 
top. 


JhieBy  lighr-gray,  compact  lime- 
beds  of  moderate  thi.-k- 
i.-si.  Contains  abundant  fossils. 
Jut  by  granite-porphyry. 


Sericite-schists.  Cut  by  granite 
and  granite-porphyry. 


GENERALIZED  COLUMNAR  SECTION  OF  THE  ROCKS  OF  THE  BISBEE  QUADRANGLE. 

FIG.  89. — Geological   section   at    Bisbee,    Arizona.     After  Ransome.     (By 
permission  of  the  Macmillan  Company,  from  Ries'  Economic  Geology.) 

were  narrow  their  walls  were  replaced,  so  that  the  vein  matter 
shades  off  into  the  country  rock. 

Arizona. — In  Arizona,  the  southern  division  of  the  Cordilleran 
region,  there  are  five  important  copper  districts.  The  Bisbee; 
Clifton-Morenci;  Globe;  Jerome,  and  Mineral  Creek.  (See  Figs. 
87  and  88.) 

(1)  The  Bisbee  district  is  situated  on  the  eastern  slope  of 
the  Mule  Mountains  and  is  only  a  short  distance  north  of  the 
international  boundary  with  Mexico.  The  ores  are  found  in 


USEFUL  METALS 


151 


faulted  strata,  ranging  from  pre-Cambrian  to  Cretaceous.  Often 
the  fault  plane  forms  a  boundary  for  the  ore  body.  The  intru- 
sions of  a  granitic  magma  have  metamorphosed  Carboniferous 
limestones  and  produced  characteristic  contact  minerals.  The 
ore-bearing  solutions  have  risen  from  unknown  depths  and  the 
ores  occur  as  replacement  deposits  in  the  limestones.  The  sur- 


NW 


Feet  above  sea  level 

4900 


Probable 
croppings 


E-pidotef 


Epidote 
/  / 


4800 


4700 


4600 


100 


Scale 


zoo 


300 feet 


FIG.  90. — Vertical  cross  section  of  the  Joy  Vein,  Clifton  Morenci  district, 
Arizona.     (After  W.  Lindgren,  U.  S.  Geological  Survey.) 

face  ores  were  originally  sulphides  of  copper,  lead  and  zinc. 
These  remain  unaltered  at  the  lower  depths  but  in  the  upper 
portions  of  the  ore  bodies  the  oxygenated  ores  of  copper,  cuprite, 
malachite  and  azurite  appear.  (See  Fig.  89.) 

(2)  The  Clifton-Morenci  District:     This  district  from  a  geo- 
logical standpoint  embraces  many  conditions  closely  related  to 


152  ECONOMIC  GEOLOGY 

those  at  Bisbee.  Mineralogically  the  conditions  differ  more  widely. 
The  geological  section  embraces  igneous  and  sedimentary  rocks 
ranging  in  age  from  pre-Cambrian  to  Quarternary.  Post-Creta- 
ceous granitic  and  dioritic  porphyries  cut  all  the  older  formations. 
The  ores  are  dependent  upon  the  porphyries  for  their  existence. 
The  ores  occur  in  the  porphyry,  or  close  to  its  contact,  or  along  dikes 
of  the  porphry  as  it  cuts  the  sedimentaries.  These  fissure  veins 
traversing  the  granite,  porphyry,  and  clastic  rocks  carry,  in  their 
unoxidized  portions,  chalcopyrite,  pyrite  and  sphalerite,  while  in 
the  oxidized  portion  the  leaching  out  of  the  copper  and  its  down- 


FIG.  91. — The  Old   Dominion  mine  and  smelter  from  the  west,   Globe, 
Arizona.     (After  F.  L.   Ransome,    U.  S.  Geological  Survey.) 

ward  transference  has  given  rise  to  secondary  chalcocite.     (See 
Fig.  90.) 

(3)  The  Globe  District:     According  to  H.  Ries,  the  ore  bodies 
occur  as  lenticular  replacements  in  limestones  and  fault  lodes, 
or  fissure  zones  in  diabase.     The  ores  in  the  upper  levels  are  of  the 
oxidized  type.     At  the  lower  levels  they  are  enriched.     Some 
bodies  of  primary  ore  with  commercial  significance  have  been 
developed.     (See  Fig  91.) 

(4)  The  Jerome  District:     The  rocks  of  this  district  are  pre- 
Cambrian  metamorphics.     The  ores  are  of  the  same  age  and  re- 
place a  schist  that  has  been  formed  by  the  intense  shearing  of  the 
basic  porphyry.     The  ores  are  bornite  and  chalcopyrite  with  a 


USEFUL  METALS 


153 


little  sphalerite.  The  percentage  of  chalcopyrite  is  higher  in  the 
alternating  bands  of  sulphide  copper  ores  and  schist  than  it  is  in 
the  more  massive  material  (Fig  92) . 


FIG.  92. — Diagrammatic  cross  section  through  the  Old  Dominion  mine 
showing  the  occurrence  of  a  mass  of  limestone  in  the  diabase  of  the  foot 
wall,  Globe  district,  Arizona.  Scale  1  in.  =200  ft.  approximately.  (After 
F.  L.  Ransome,  U.  S.  Geological  Survey.) 

(5)  The  Mineral  Creek  District:  The  terranes  are  pre-Cam- 
brian  and  the  ore  is  chalcocite  widely  disseminated  through  the 
schistose  rocks. 

(4)  The  Pacific  Coast  Belt. — California  is  the  largest  producer 


154 


ECONOMIC  GEOLOGY 


of  copper  in  this  western  belt.  The  most  important  field  is  near 
the  northern  end  of  the  Sacremento  Valley  in  Shasta  County. 
The  ore  occurs  in  Permo-Carboniferous  and  Triassic  lavas  and 
tuffs.  The  ores  are  of  the  sulphide  type  and  the  lodes  vary  from  a 
few  inches  to  hundreds  of  feet  in  width. 

Chalcopyrite,  chalcocite  and  bornite  occur  in  the  Iron  Moun- 
tain district  as  impregnation  deposits  in  a  zone  of  crushed  brec- 
cias in  rhyolite.  Chalcopyrite,  pyrite,  quartz  and  barite  occur 
in  the  Bully  Hill  district  in  a  sheared  zone  following  a  dike  of 


Scale 


jo feet 


Schist 


FIG.  93 .- — Ferris-H agger ty  mine,  Bonanza  stope,  Encampment  district, 
Wyoming,  showing  form  of  the  ore  body.  (After  A.  C.  Spencer,  U.  S. 
Geological  Survey.) 


diabase.  The  ore  lies  either  in  the  dike  or  at  the  contact  with 
rhyolite.  Chalcopyrite  and  pyrite  occur  in  lens-shaped  masses 
in  the  metamorphic  slates  and  schists  in  the  foothills  of  the  Sierra 
Madre  Mountains. 

The  Bingham  Disrtict,  Utah:  According  to  E.  T.  Hancock, 
this  field  includes  an  oblong  area  of  about  24  square  miles.  It  lies 
between  the  Jordon  Valley  on  the  east  and  the  Oquirrh  range  of 
mountains  on  the  west.  The  terranes  are  Carboniferous  quartz- 
ites  and  limestones  that  have  suffered  extensive  intrusion,  intense 
fissuring,  and  partial  burial  beneath  an  andesite  flow.  The  ore 


USEFUL  METALS 


155 


bodies  are  centered  in  the  localities  which  have  undergone  the 
most  extensive  intrusion  and  fissuring. 

The  copper  ore  occurs  in  flat  lenses  in  the  metamorphosed  lime- 
stones. In  the  Highland  Boy  mine  there  are  large  lenticular 
bodies  of  chalcopyrite  in  the 
fissured  marble  adjacent  to 
the  intrusives.  The  ore  oc- 
curs disseminated  through  the 
igneous  rocks,  and  limestone. 

According  to  J.  M.  Bout- 
well,  heated,  aqueous,  min- 
eral-bearing solutions,  rich  in 
carbon  dioxide  and  potassium 
oxide,  rose  along  strong  north- 
east and  southeast  fracture 
zones,  altered  their  walls  by 
adding  quartz  to  quartzite, 
impregnating  marble  with 
metallic  sulphides  and  specu- 
lar iron  ore,  and  silicifying, 
seriticizing,  and  impregnating 
monzonite  with  metallic  sul- 
phides and  depositing  lode 
ores  in  largest  volume  between 
calcareous  and  carbonaceous 
walls,  mainly  by  filling,  and 
partially  by  replacement. 
The  same  author  furthermore 
states  that  "it  is  probable 
that  the  principal  scource  of 
the  copper  ore  in  the  lime- 
stone was  the  magma  of  the 
intrusive,  that  the  mineral 
elements  were  transported  by 
the  intrusives  and  by  the 
thermal  solutions  and  vapors  £ 
emitted  from  both  their  super- 
ficial and  deeper  portions  and  that  the  ore  was  deposited  by 
molecular  replacement  of  a  metamorphosed,  at  least  partially 
marmorized  and  silicified,  country  rock"  (Figs.  93  and  94). 

(5)  The  Alaskan  District. — In  Alaska  there  are  four  distinct 


156 


ECONOMIC  GEOLOGY 


copper  fields  or  districts.  The  Prince  of  Wales  Island;  Prince 
William  Sound;  Copper  River  district,  and  the  Kotsina  district. 
(See  Fig.  95.) 

(1)  On  Prince  of  Wales  Island,  contact  metamorphic  ores 
occur  in  irregular  masses  along  the  contacts  of  the  intrusives  with 
limestones.  The  copper  mineral  is  chalcopyrite.  It  is  associ- 


FIG.  95. — Geologic  map  of  Copper  Mountain  Region,  Prince  of  Wales 
Island,  Alaska.  After  Wright.  (By  permission  of  the  Macmillan  Company, 
from  Ries*  Economic  Geology.} 


ated  with  pyrrhotite,  pyrite  and  magnetite  with  a  gangue  of  am- 
phibole  and  feldspar.  Fissure  veins  and  disseminated  ores  are 
also  encountered.  (See  Fig.  96.) 

(2)  On  Prince  William  Sound  the  ore  is  chalcopyrite  dissemi- 
nated through  the  metamorphic  schists.  The  ore  is  associated 
with  pyrite  and  pyrrhotite  in  cavity  fillings.  Also  as  replace- 


USEFUL  METALS 


157 


ment    deposits   of   impregnations   in   a   shear   zone   in   slates 
and  graywackes. 

(3)  The  Copper  River  district  is  near  Mount  Wrangell.     The 
ores  are  chalcocite  and  bornite  associated  with  pyrrhotite  and 
magnetite  as  dissemination  deposits  in  masses  of  greenstone. 

(4)  The  Kotsina  district  is  situated  some  little  distance  in- 
land from  the  coast.     The  chief  copper  mineral  is   chalcocite. 


Limestone 
&  Quartz  ite 


Schist  A 
Greenstone 


FIG.  96. — Sketch  map  of  the  Copper  Mountain  district,  Prince  of  Wales 
Island,  Alaska.  (After  F.  E.  and'C.  W.  Wright,  U.  S.  Geological  Survey.) 

The  ore  is  found  as  replacement  deposits  in  the  Triassic  lime- 
stones associated  with  the  earlier  greenstones. 

The  Geographical  Horizon. — Copper  ores  are  not  restricted 
to  the  rocks  of  any  particular  age.  They  occur  in  all  horizons 
up  to  the  Tertiary,  but  the  ores  are  especially  abundant  in  the 
older  formations  as  the  pre-Cambrian,  Cambrian  and  Ordovician 
terranes. 

Methods  of  Extraction.  (1)  The  Reduction  Process. — Copper 
is  extracted  from  its  carbonates  and  oxides  by  means  of  roasting 


158  ECONOMIC  GEOLOGY 

the  ore  in  the  presence  of  carbon.  The  following  equations 
indicate  the  process  as  applied  to  cuprite  and  tenorite : 

Cu20+C  =  CO+2Cu 
2CuO+2C  =  2CO+2Cu. 

The  two  carbonates,  malachite  and  azurite,  when  roasted  lose 
both  water  and  carbon  dioxide.  The  resulting  product  is  the 
black  oxide  of  copper,  which  in  the  presence  of  carbon  yields 
metallic  copper  and  carbon  monoxide  according  to  the  equation 
given  under  tenorite. 

(2)  The  Oxidation  Process. — The  sulphides  of  copper  are  roasted 
in   large    beds   in   the   open    air  to  volatilize  the  sulphur  con- 
tent as  sulphur  dioxide.     These  beds  at  the  Ely  mine  at  Copper- 
field  in  Vershire,  Vermont,  in  the  days  when  1700  miners  were  em- 
ployed at  one  time,  were  approximately  50  rods  in  length  and 
about  4  ft.  high.     The  copper  by   the    open-air   roasting   was 
largely  converted  into  the  oxide.     In  the  later  years  at  the  same 
camp  the  ore  was  roasted  in  a  blast-furnace  and  the    sulphur 
passed  out  of  the  chimney  flues  as  sulphur  dioxide.     The  con- 
centrated and  oxidized  ore  is  then  roasted  with  carbon  or  coke 
and  copper  matte  is  obtained.     From  the  matte  by  further 
treatment  blister  copper  is  obtained,  from  which  arsenic  and 
antimony  are  removed  by  volatilization,  if  present,  then  the  lead, 
then  the  iron,  and  the  copper  is  finally  obtained  in  a  compara- 
tively pure  state  and  cast  into  blocks  weighing  about  200  Ib. 

(3)  The  Chlorination  Process. — When  copper  ores  contain  about 
3  per  cent,  of  copper,  too  poor  for  the  extraction  of  copper  by 
roasting  alone,  they  are  sometimes  calcined  with  about  15  per 
cent,  of  common  salt.     This  converts  all  the  copper  into  the 
chloride  which  is  readily  soluble  in  water.     The  fused  mass  is 
then  leached  with  water  and  the  resulting  solution  of  the  chloride 
of  copper  is  drawn  off  into  precipitating  tanks.     Scrap  iron  is 
often  used  to  reduce  the  copper  to  the  elemental  state. 

(4)  The  Electrolytic  Process. — This  process  consists  in  bringing 
the  copper  into  solution  and  reducing  the  metal  by  electroly- 
sis.    The  process  is  applicable  to  the  forsaken  residues  around 
many  old  copper  mines.     The  cost  of  reduction  is  said   to   be 
about  one-half  cent  per  ton  of  solution. 

(5)  The  Scrap-iron  Process. — The  Rio  Tinto  mines  in  Spain 
furnish  many  pounds  of  copper  by  simple  reduction  with  scrap 
iron.     At  Wicklow,  Ireland,  at  one  time  about  500  tons  of  scrap 


USEFUL  METALS  159 

iron  was  introduced  into  the  mine  waters  bearing  copper  sul- 
phate. In  one  year  the  iron  was  all  dissolved.  Each  ton  of 
iron  produced  from  one  and  a  half  to  two  tons  of  cement  copper, 
a  kind  of  reddish  mud  containing  1600  Ib.  of  copper  in  every 
ton.  There  are  many  other  niethods  of  treating  copper  ores 
as  suggested  and  described  in  " Modern  Copper  Smelting"  by 
E.  D.  Peters. 

Large  quantities  of  pyrite  containing  small  amounts  of  copper 
are  annually  imported  from  Spain.  The  sulphur  content  is  used  in 
the  manufacture  of  sulphurous  and  sulphuric  acids.  The  residue  is 
concentrated  and  smelted  into  pig  copper  which  is  electrolytically 
refined.  Small  amounts  of  copper  in  these  Spanish  ores  can  be 
extracted  with  profit  in  America,  The  refineries  also  treat  ores 
imported  from  Mexico,  Australia,  Tasmania  and  Japan.  There 
is  an  interesting  incident  cited  by  James  Douglas  where  copper 
matte  was  bought  at  full  price  in  Tennessee,  transported  by  rail 
to  Norfolk,  Virginia,  reshipped  to  Tampico,  Mexico,  carried 
half  way  across  the  Republic,  used  in  the  extraction  of  gold  and 
silver,  concentrated  into  black  copper  oxide,  brought  back  again 
by  rail  and  water  to  New  Jersey,  and  electrolytically  refined 
with  profit.  The  low  transportation  rates  and  precipitation  by 
electrolysis  at  the  expenditure  of  less  than  1/2  cent  per  pound 
makes  this  possible.  Chilian  copper  bars  stored  in  English 
warehouses  have  been  shipped  to  the  United  States  refineries 
for  electrolytic  treatment,  and  the  refined  product  exported  to 
Europe.  The  refineries  can  not  only  successfully  compete  with 
those  abroad,  but  with  them  also  in  their  own  marts  of  trade, 
for  copper  refining  costs  less  in  America  than  in  Europe  because 
our  refineries  are  larger,  better  equipped,  and  more  economically 
managed. 

Uses  of  Copper. — The  uses  of  copper  in  the  various  arts  and 
industries  are  almost  too  familiar  to  mention.  Some  of  the 
salts  of  copper  are  used  in  medicine  and  the  sulphate  of  copper 
is  widely  utilized  in  the  purification  of  water  supplies  for  villages 
and  cities.  It  destroys  the  euroglena  americana  and  other  organ- 
isms in  the  storage  waters  that  give  to  them  a  fishy  taste  and 
odor. 

Copper  is  used  extensively  in  the  various  forms  of  electrical 
apparatus,  electric  traction  and  power,  in  electrotyping,  electric 
lighting,  telegraph  cables,  in  flashing  around  chimneys  and  in 
gutters.  The  alloys  of  copper  are  of  great  technical  value  and 


160  ECONOMIC  GEOLOGY 

capable  of  wide  industrial  application.  Copper  has  been  used 
as  a  medium  of  exchange  for  many  generations.  In  coinage, 
gold  and  silver  are  too  soft  to  resist  abrasion.  They  are  each 
alloyed  with  copper  in  such  proportions  that  the  color  and  mal- 
leability are  not  seriously  impaired,  while  the  hardness  is  ma- 
terially increased.  Copper  is  the  hardening  metal  in  the  gold 
and  silver  of  jewelry.  With  platinum  copper  alloys  in  all  pro- 
portions. Cooper's  gold,  which  so  closely  resembles  18  carat 
gold  and  for  which  it  is  so  largely  substituted,  sometimes  con- 
tains over  80  per  cent,  of  copper.  Mirror  metal  has  57.85  per 
cent,  copper  and  pen  metal  13  per  cent,  of  copper. 

The  brasses  are  important  alloys  of  copper  and  zinc.  They 
range  from  95  per  cent,  of  copper  and  5  per  cent,  of  zinc  to  40 
per  cent,  of  copper  and  60  per  cent,  of  zinc.  The  most  import- 
ant brasses  are  those  of  about  40  per  cent,  of  copper  and  60  per 
cent,  of  zinc.  Some  of  these  have  a  tensile  strength  of  40,000 
Ib.  to  the  square  inch.  English  brass  consists  of  2  parts  of 
copper  and  one  of  zinc.  Muntz  metal  consists  of  3  parts  of  copper 
and  one  of  zinc.  Dutch  brass  consists  of  5  parts  of  copper  and 
one  of  zinc.  Brazing  metal  of  9  parts  of  copper  and  one  of  zinc. 
Naval  brass  which  is  so  extensively  used  in  condenser  tubes 
consists  of  70  per  cent,  copper,  29  per  cent,  zinc,  and  one  part 
of  tin. 

The  bronzes  are  important  alloys  of  copper  and  tin.  Various 
forms  of  bronze  were  used  by  the  ancient  Greeks  and  Romans. 
Relics  of  bronze  have  been  found  in  the  Lake  dwellings  of  Switzer- 
land. The  bronzes  of  the  greatest  technical  value  carry  over 
80  per  cent,  of  copper.  Those  containing  about  50  per  cent,  of 
copper  are  called  speculum  metal,  which  is  used  for  widely  dif- 
ferent purposes  than  the  regular  bronzes,  as,  for  instance,  the 
silvering  of  glass  reflectors  and  the  specula  for  reflecting  telescopes. 
Gun  metal  consists  of  9  parts  of  copper  and  1  part  of  tin. 
Bell  metal  consists  of  80  per  cent,  copper  and  20  per  cent,  of  tin. 
Silver  is  sometimes  added  in  small  quantities  to  bell  metal  to 
increase  its  sonorous  quality.  '  Machinery  brasses  and  bronzes 
consist  of  alloys  of  copper,  tin  and  zinc. 

Copper  is  used  largely  as  bearing  metals.  One  of  these  con- 
sists of  70  per  cent,  copper,  15  per  cent,  of  tin,  and  15  per  cent,  of 
lead.  It  is  well  known  and  widely  utilized.  Another  consists 
of  7  parts  of  copper  and  one  of  tin.  Still  another  of  65  parts  of 
copper  and  35  parts  of  tin.  Hot  boxes  upon  railroad  trains  often 


USEFUL  METALS  161 

arise  from  the  segregation  of  the  copper  in  the  alloy  into  spots. 
Hot  boxes  may  arise  from  three  causes:  (1)  Segregation  of  the 
metal  into  spots  capable  of  producing  intense  heat  through  fric- 
tion; (2)  too  coarse  a  crystalline  structure  of  the  alloy,  and  (3) 
the  presence  of  dross.  Imperfect  lubrication  plays  a  very  minor 
part. 

Aluminum  bronze  as  the  name  implies  is  an  alloy  of  copper 
and  aluminum.  These  various  alloys  are  widely  used  in  the  arts. 
One  of  these  consist  of  90  per  cent,  copper  and  10  per  cent,  of 
aluminum.  If  the  percentage  of  aluminum  falls  below  5  or  rises 
above  10  the  bronzes  are  of  little  techincal  value. 

Copper  amalgams  are  used  wherever  a  change  from  a  plastic 
to  a  solid  state  is  desired.  They  are  used  to  some  extent  in  filling 
teeth. 

One  of  the  new  uses  to  which  copper  has  been  successfully 
applied  is  the  coating  of  railroad  passenger  cars,  forming  a  sub- 
stitute for  paint  and  varnish.  The  sheet  copper  used  on  the  sides 
is  0.012  in.  in  thickness  and  fastened  to  the  wood  by  invisible 
screws.  When  in  place  the  copper  is  washed  with  a  weak  acid 
solution,  and  the  shellaced  or  lacquered. 

Copper  oxide  has  come  into  a  new  use  in  the  painting  of  the 
bottom  of  ships.  This  forms  a  substitute  for  copper  sheathing. 
Copper  oxide  is  used  in  refining  petroleum.  The  gas  is  absorbed 
by  the  copper  oxide  forming  the  sulphide  of  copper  and  water. 
The  oxide  is  regenerated  by  roasting  the  sulphide.  Cupric  oxide 
is  used  in  the  Edison  LeLande  electric  battery,  which  consists 
of  a  zinc  element  and  one  of  copper  oxide.  The  battery  is  said 
to  be  one  of  the  most  economical  and  durable  in  the  American 
market.  Cupric  oxide  is  used  also  in  coloring  glass,  the  green 
and  the  blue  depending  largely  upon  the  manipulation.  Copper 
oxide  is  used  in  the  tile  and  glazed  brick  industries  for  decorative 
effect.  It  is  also  used  in  the  oxidation  of  organic  matter  for  it  is 
an  efficient  oxidizing  agent  under  heat. 

The  output  of  copper  in  1906  was  $177,595,888.  The 
smelter  production  of  copper  in  1911  in  the  United  States  ex- 
ceeded 1,000,000,000  Ibs. 

Cadmium:  Its  Properties,  Occurrences  and  Uses 

Properties. — Cadmium,  symbol  Cd,  is  a  bluish  white,  ductile, 

malleable  and  sectile  metal.     It  tarnishes  upon  exposure  to  the 
11 


162  ECONOMIC  GEOLOGY 

atmosphere,  but  when  freshly  cut  its  luster  is  very  brilliant.  It 
is  readily  soluble  in  the  mineral  acids.  Its  specific  gravity  is 
8.6,  melting  point,  321.7°  C.,  and  its  atomic  weight  is  112.4. 

Ores  of  the  Metal. — Cadmium  does  not  occur  free  and  uncom- 
bined  in  nature.  It  must,  therefore,  occur  only  in  combination. 
The  one  important  mineral  is  the  yellow  sulphide,  greenockite, 
CdS.  This  ore  occurs  in  association  with  sphalerite,  ZnS,  and 
as  an  incrustation  on  calcite,  CaCOs.  The  resinous  luster  of 
cadmif erous  sphalerite  has  often  been  attributed  to  the  presence  of 
greenockite.  Cadmium  occurs  also  in  combination  with  carbonic 
acid  as  cadmium  carbonate,  CdCOs,  and  in  smithsonite,  ZnCOs. 

Origin  of  the  Ores. — Cadmium  ores  are  always  of  secondary 
origin.  They  are  deposited  from  solution  with  the  ores  of  zinc 
by  the  action  of  alkaline  sulphides  upon  ascending  solutions  of 
the  metal.  The  metal  may  also  be  precipitated  as  the  sulphide 
with  the  sulphide  of  zinc  by  the  action  of  organic  matter.  By 
the  alteration  of  cadmiferous  sphalerite  in  the  upper  level  of 
ore  bodies,  cadmiferous  smithsonite  would  be  formed  as  a  surface 
deposit. 

Geographical  Distribution. — Greenockite  occurs  in  associa- 
tion with  zinc  in  Arkansas,  Kansas  and  Missouri.  It  occurs  also 
in  Pennsylvania  where  it  is  associated  with  the  yellow  zinc  car- 
bonate known  by  the  miners  as  " turkey  fat." 

Geological  Horizon. — The  ores  of  cadmium  are  not  confined 
to  any  particular  geological  horizon.  They  are,  in  fact,  the  same 
as  that  of  zinc. 

Method  of  Extraction. — The  manufacture  of  metallic  cadmium 
was  begun  for  the  first  time  in  the  United  States  in  1907  by  the 
Grasselli  Chemical  Company,  Cleveland,  Ohio.  The  process  is 
fractional  distillation  in  iron  retorts.  The  brown  fumes  that 
distill  over  in  the  first  product  from  the  refining  of  zinc  are  cad- 
mium oxide,  CdO. 

Usfcs  of  Cadmium. — Cadmium  is  used  to  some  extent  in  the 
manufacture  of  yellow  pigments.  The  iodide  and  bromide  of 
cadmium  are  used  in  photography.  Cadmium  is  used  extensively 
in  the  manufacture  of  sterling  silverware.  In  this  industry  0.5 
per  cent,  of  cadmium  imparts  malleability  to  the  alloy  and  pre- 
vents the  formation  of  blisters.  Cadmium  alloys  all  possess  a 
low  melting  point.  Many  of  these  alloys  of  cadmium,  bismuth, 
lead  and  tin  in  varying  proportions  melt  between  60°  and  100°. 
Stereotype  metal  consists  of  50  per  cent,  lead,  27.5  per  cent,  tin 


USEFUL  METALS  163 

and  22.5  per  cent,  cadmium.  Cadmium  is  used  also  in  the 
britannia  ware  and  soldering  German  silver.  A  soft  solder  con- 
sisting of  37  parts  lead  and  63  parts  tin,  and  8  parts  cadmium 
fuses  at  36°.  Cadmium  is  used  also  in  cadmium  plating,  especi- 
ally with  tin,  where  the  coating  is  hard  and  takes  a  high  polish. 
Cadmium  is  used  somewhat  with  mercury  as  an  amalgam  in  the 
filling  of  teeth.  Cadmium  salts  are  well  known  in  the  chemical 
trade. 


CHAPTER  VI 
USEFUL  METALS  CONTINUED  (GROUP  II,  SUBGROUP  B) 

ARSENIC,  ANTIMONY,  TIN 
Arsenic:  Its  Properties,  Occurrence  and  Uses 

Properties. — Arsenic,  symbol  As,  is  a  steel  gray,  brittle  metal- 
loid. It  crystallizes  in  the  hexagonal  system  in  regular  acicular 
prisms,  and  begins  to  volatilize  at  100°  with  a  characteristic 
garlic  odor.  It  is  a  good  conductor  of  heat  and  electricity.  In 
its  salts  it  suggests  an  acid,  and  in  its  alloys  a  metal.  It  is 
seldom  that  it  plays  the  role  of  a  base.  It  is  soluble  in  HC1; 
specific  gravity,  5.8,  melting  point,  at  red  heat,  and  its  atomic 
weight  is  75. 

Ores  of  Arsenic. — Native  arsenic,  100  per  cent.  As.  Often  al- 
loyed with  gold  and  silver,  sometimes  with  bismuth  and  iron. 

Realgar,  AsS,  70.1  per  cent.  As.  The  only  aurora  red  mineral 
entirely  volatile  before  the  blow  pipe. 

Orpiment,  As2S3,  61  per  cent.  As.  With  honey  yellow  surfaces 
on  its  cleavage  face. 

Arsenopyrite,  FeAsS,  46  per  cent.  As.     A  sulph-arsenide  of  iron. 

Arsenolite,  As203,  75.8  per  cent.  As.  A  white  oxidation  prod- 
duct  of  other  ores. 

Lollingite,  FeAs2,  72.8  per  cent.  As. 

Leucopprite,  Fe3As4,  62.1  per  cent.  As. 

Smaltite,  CoAs2,  71.8  per  cent.  As. 

Niccolite,  NiAs,  76.1  per  cent.  As. 

Allemontite,  SbAs3,  65.2  per  cent.  As. 

There  are  also  many  arsenates  of  the  useful-  and  rare  metals, 
also  the  arsenate  of  calcium. 

Origin  of  the  Ores. — Arsenic  is  one  of  the  rarer  elements, 
although  widely  distributed  in  nature.  It  has  been  found  in 
the  nails  of  man,  in  the  horns  and  hoofs  of  cattle,  in  the  mane 
and  hoofs  of  horses,  and  in  the  bristles  and  hoofs  of  hogs.  Ac- 
cording to  F.  W.  Clarke,  traces  of  arsenic  have  been  observed  in 

164 


USEFUL  METALS  165 

organic  matter  and  found  as  a  common  ingredient  of  thermal 
springs.  It  has  been  detected  by  Daubree*  and  Gautier  in  sea 
water.  Native  arsenic  may  result  from  the  decomposition  and 
reduction  of  other  ores  of  arsenic.  W.  H.  Weed  and  L.  V. 
Pirsson  report  both  realgar  and  orpiment  from  the  hot-spring  de- 
posits of  Yellowstone  Park.  G.  F.  Becker  observed  the  sul- 
phides of  arsenic  in  a  sinter  at  Steamboat  Springs,  Nevada. 
They  occur  in  seams  in  a  sandy  clay  beneath  the  lava  of  Iron 
County,  Utah.  Arsenic  has  been  found  in  calcite  in  California, 
and  orpiment  has  been  deposited  in  quartz  crystals  in  Bosnia. 
In  Tyrol  the  sulphides  of  arsenic  occur  in  association  with 
gypsum.  Near  Naples  arsenic  occurs  as  a  product  of  volcanic 
sublimation.  Realgar  and  orpiment  have  both  been  found  as 
sublimation  products  of  burning  coal  mines. 

The  ready  solubility  of  the  sulphides  of  arsenic  allows  trans- 
portation to  a  considerable  distance  from  the  original  ore  bodies 
only  to  be  reprecipitated  through  various  agencies.  Arseno- 
pyrite  is  sparingly  soluble  in  warm  waters  and  from  these  solu- 
tions it  is  known  to  recrystallize.  Arsenolite,  the  white  oxide 
of  arsenic,  is  an  oxidation  product  of  the  native  element  or  of 
other  ores  of  arsenic.  Percolating  arsenical  solutions  acting 
upon  the  carbonates  of  other  metals  or  upon  calcite  would  give 
rise  to  the  arsenates  of  those  metals  or  the  arsenate  of  calcium. 

Character  of  the  Ore  Bodies. — Native  arsenic  occurs  in  veins 
in  the  crystalline  rocks  and  the  older  schists.  It  is  often  asso- 
ciated with  ruby  silver,  antimony  and  the  sulphide  of  zinc. 
The  sulphides  occur  in  fissure  veins  with  silver  and  lead  minerals, 
also  in  seams  in  sandy  clays  and  as  small  crystals  embedded  in 
clay.  (See  Fig.  97.) 

Arsenopyrite  is  by  far  the  most  important  ore.  It  occurs 
in  well-defined  fissure  veins  in  beds,  in  threaded  bands,  and  as 
impregnation  deposits  in  the  country  rock. 

Geographical  Distribution. — As  already  noted  the  arsenical 
minerals  are  widely  distributed  in  nature  but  the  valuable  com- 
mercial occurrences  are  few.  In  the  United  States  the  areas 
fall  into  three  distinct  belts:  (1)  The  Appalachian  belt;  (2) 
the  Cordilleran  district,  and  (3)  the  Pacific  Coast  belt. 

(1)  The  Appalachian  belt  stretches  from  Alabama  on  the 
south  in  a  northeasterly  direction  to  Newfoundland.  According 
to  H.  Ries,  one  of  the  best  known  deposits  of  arsenopyrite  occurs 
at  Rewald,  Floyd  County,  Virginia.  The  ore  deposit  forms  a 


166 


ECONOMIC  GEOLOGY 


series  of  lenses  in  a  quartz-sericite  schist.  The  principal  lens 
is  about  3  ft.  wide  at  the  surface  but  thickens  to  14  ft.  at  a 
depth  of  120  ft.  An  unworked  deposit  of  arsenopyrite  also 
occurs  in  the  same  state  in  Rockbridge  County  in  association 
with  pyrite  and  cassiterite  in  quartz-greisen  bearing  tin  veins. 

At  Carmel,  New  York,  arsenopyrite  occurs  as  a  banded  deposit 
in  gneiss,  in  two  zones  20  ft.  wide  intersecting  each  other  at 
an  angle  of  60  degrees.  At  Braintree,  Vermont,  there  is  a  4-ft. 


w 


FIG.  97. — Vertical  section  in  short  drift  near  end  of  upper  tunnel,  Great 
Gluch  mine,  Mineral  Ridge,  Nevada.  A,  Alaskite;  Q,  quartz;  Q',  quartz 
(f  eldspathic,  much  broken) ;  S,  shaley  limestone ;  M,  mispickel  ore.  Mispickel 
occurs  along  a  fault  zone  on  both  sides  of  the  crushed  quartz  especially 
abundant  on  the  hanging  wall  side.  (After  J.  E.  Spurr,  U.  S.  Geological 
Survey.) 

vein  of  arsenopyrite  traversing  Ordovician  limestones  and 
schists.  Arsenopyrite  occurs  in  fine  crystallizations  in  gneiss 
at  Franconia,  New  Hampshire,  also  at  Jackson  and  Haverill, 
New  Hampshire. 

(2)  The  Cordilleran  district   carries  many  gold,  copper  and 
other  mineral  deposits  that  contain  arsenic  but  in  the  roasting 
and  smelting  of  these  ores  the  arsenic  is  not  saved  as  a  by-product 
but  is  allowed  to  pass  off  with  the  furnace  smoke  and  gases. 

(3)  The  Pacific  coast  belt    has    two    chief    representatives. 


USEFUL  METALS  167 

One  in  the  arsenical  gold  ores  of  California  and  the  other  at 
Monte  Cristo,  Washington,  where  auriferous  sulphides,  realgar 
and  orpiment  are  mined  and  the  white  arsenic  of  commerce  is 
manufactured. 

At  Deloro,  Ontario,  arsenopyrite  occurs  in  large  beds  with  a 
quartz  gangue  cutting  pre-Cambrian  schists.  This  deposit  has 
been  successfully  worked  for  some  time  both  for  gold  and  for 
the  arsenic  which  is  converted  into  white  arsenic.  The  ore  also 
occurs  in  fissure  veins  with  a  quartz  gangue  in  Grimsthorpe, 
Ontario.  The  ores  here  are  not  so  highly  auriferous  as  at 
Deloro. 

According  to  Thomas  and  MacAlister,  the  presence  of  arsenical 
pyrites  in  some  of  the  largest  tin  mines  of  the  west  of  England 
is  remarkable.  The  lodes  belong  to  the  pneumatolytic  group  of 
ores.  Under  similar  circumstances  the  ore  is  found  in  the  tin 
mines  of  Saxony  and  Bohemia.  Workable  deposits  of  arsenical 
ores  are  found  also  in  Turkey. 

Geological  Horizon. — Arsenical  ores  are  found  from  the  pre- 
Cambrian  to  the  Ordovician  in  the  modes  of  occurrence  suggested. 
Recent  arsenical  deposits  are  not  of  workable  dimensions. 

Methods  of  Extraction.  The  Roasting  Process . — Native  arsenic 
and  its  sulphides  are  crushed  and  heated  in  long  earthenware 
retorts  into  whose  mouths  are  fitted  earthenware  receivers.  The 
arsenic  volatilizes,  and  condenses  as  a  compact  crystalline  solid. 
This  product  is  redistilled  in  a  current  of  air  when  the  arsenic 
is  converted  into  the  white  oxide,  the  form  in  which  it  generally 
appears  in  the  marts  of  trade. 

The  Electric  Furnace  Process. — The  Arsenical  Ore  Reduction 
Company  of  Newark,  New  Jersey,  has  established  anelectrical  fur- 
nace for  the  treatment  of  arsenopyrite,  commercially  known  as  mis- 
pickel.  The  ore  is  subjected  to  the  intense  heat  of  the  furnace  in 
an  atmosphere  of  nitrogen.  The  iron  present  in  the  arsenopyrite 
unites  with  the  sulphur  in  the  formation  of  a  ferrous  sulphide, 
which  is  drawn  off  as  a  liquid  mass.  The  arsenic  is  distilled  and 
condensed  as  a  white  powder.  The  cost  of  the  treatment  of 
such  ores  with  46  per  cent,  of  arsenic  is  estimated  to  be  less  than 
25  cents  per  hundred  weight. 

Sources  of  the  Arsenic  of  Commerce. — (1)  Arsenic  is  obtained  as 
a  by-product  in  the  treatment  of  the  ores  from  various  tin  mines, 
especially  in  England.  (2)  From  tin,  copper  and  tungsten  ores 
intimately  associated  with  arsenic.  (3)  From  the  treatment  of 


168  ECONOMIC  GEOLOGY 

the  waste  heaps  of  exhausted  copper  mines.  (4)  Some  mines  are 
worked  solely  for  the  arsenopyrite  which  they  contain.  The 
mineral  is  then  concentrated,  not  roasted,  and  sold  direct  to  the 
refineries.  (5)  Some  mines  are  worked  for  the  arsenopyrite  which 
is  concentrated  and  manufactured  into  commercial  white  arsenic 
at  the  mine. 

In  the  arsenic  industry  various  samples  of  the  roasted  ore  are 
analyzed  in  order  to  keep  the  product  uniform  in  arsenic  content. 
For  any  arsenic  found  above  a  fixed  minimum  the  men  are  sub- 
jected to  a  reduction  in  their  wages.  Good  work  is  the  result. 
Arsenic  is  obtained  from  speiss  that  is  formed  in  lead  furnaces. 
This  is  said  to  have  been  the  source  of  the  arsenic  sometimes 
present  in  sulphuric  acid. 

Uses  of  Arsenic. — Arsenical  compounds  have  acquired  great 
notoriety  because  murderers  and  suicides  have  successfully  re- 
sorted to  them  to  accomplish  their  foul  designs.  Their  toxic 
nature  has  become  so  pronounced  that  not  only  the  general  pub- 
lic but  scientific  and  medical  circles  have  become  accustomed  to 
avoid  such  substances  and  to  overlook  some  of  the  good  qualities 
which  arsenic  possesses.  The  layman  knows  very  little  of  the 
sources  of  the  arsenic  supply,  of  the  manufacture  of  arsenical 
compounds,  and  of  the  properties  of  the  finished  product. 

Arsenic  is  used  in  producing  colors  too  extensively  utilized  for 
the  public  good.  Potassium  arsenite  was  formally  used  for  tinting 
wall  paper.  This  use  is  now  practically  controlled  by  law,  only 
a  minimum  per  cent,  per  square  yard  of  wall  paper  is  permissible. 
From  dampness  or  other  causes  a  mould  is  developed  and  hydro- 
gen is  set  free  which  reacts  upon  the  arsenical  compound  in  the 
paper  and  forms  the  deactty  arsenureted  hydrogen,  AsH3. 

Arsenic  is  used  in  the  calico  printing  as  a  conveyor,  or  fixer,  or 
both,  of  the  aniline  colors.  It  does  not  enter  into  the  color  largely 
if  at  all  for  it  is  washed  out  of  the  calico  during  the  process  of 
coloring.  Some  attempts  have  been  made  to  recover  the  arsenic 
from  the  resulting  solution  but  the  processes  instituted  are  too 
expensive.  Realgar  is  utilized  in  the  various  red  shades  of 
fabrics,  orpiment  in  the  production  of  various  shades  of  yellow. 
Grays  may  also  contain  arsenic.  Perhaps  the  most  dreaded  of  all 
colors  on  account  of  its  arsenic  is  the  terra  cotta  red.  Various 
parties  concerned  directly  in  the  manufacture  of  tinted  papers 
and  colored  fabrics  either  mine  or  import,  or  both,  realgar  and 
orpiment  for  use  as  a  pigment  in  their  industries. 


USEFUL  METALS  169 

Arsenic  is  used  in  medicine  in  several  forms.  Liquor  arseni- 
cales  is  used  in  intermittent  fevers,  in  rheumatism  and  nervous 
afflictions.  White  arsenic  is  used  extensively  in  progressive, 
pernicious  anemia.  Two  to  four  grains  of  arsenic  form  a  fatal  dose. 
Arsenic  is  used  also  in  many  embalming  fluids.  In  arsenic  eaters 
it  clarifies  the  skin  and  imparts  a  rotundity  to  the  body.  It  also 
strengthens  the  respiration,  therefore,  Marathon  runners  and 
mountain  climbers  have  resorted  to  its  use. 

Fowlers  solution  is  used  to  fatten  horses  and  to  give  them  greater 
speed  in  the  race.  It  furnishes  not  only  rotundity  to  the  body, 
but  also  produces  glossy,  shiny  hair. 

Arsenic  is  used  in  many  forms  as  a  preservative.  Ten  parts  of 
hot  water  or  30  parts  of  cold  water  will  dissolve  1  part  of  white 
arsenic.  The  solution  is  a  good  wood  preservative  as  it  prevents 
both  wet  and  dry  rot.  It  is  important  in  the  treatment  of  rail- 
way ties,  telephone  and  telegraph  poles,  and  the  timber  of 
mines.  Carpenters  and  builders  use  it  in  many  forms  of  joints. 

Arsenic  is  used  extensively  in  agriculture.  Hundreds  of  tons 
of  arsenic  are  used  annually  as  a  weed  killer.  It  is  used  exten- 
sively to  prevent  foot  rot  in  sheep.  The  white  arsenic  is  dis- 
solved in  water  and  poured  into  troughs  20  ft.  long  and  li  ft. 
wide.  The  sheep  are  driven  back  and  forth  through  the  trough 
and  then  on  to  dry  ground  or  floors  that  their  feet  may  thoroughly 
dry.  Arsenic  is  used  for  killing  sheep  ticks,  both  the  sheep  and 
lambs  being  dipped  in  a  solution  of  white  arsenic. 

Arsenic  is  used  as  an  insecticide  as  lead  arsenate  in  the  de- 
struction of  the  gypsy  moth.  Large  quantities  of  Paris  green  are 
manufactured  annually  to  kill  the  Colorado  beetles  and  their 
slugs;  also  the  larvae  on  currant  bushes,  rose  bushes,  and  cabbages. 
In  England  the  best  crops  of  potatoes  are  always  obtained  in  the 
vicinity  of  an  arsenical  plant.  Arsenic  successfully  checks  potato 
blight  and  in  many  modifications  it  is  used  for  that  purpose  in 
America. 

Arsenic  is  used  in  rat  poison  and  fly  paper.  Much  arsenic  has 
been  sent  across  the  mountains  of  South  America  on  mule  back 
for  the  dressing  of  hides  for  exportation.  It  effectually  prevents 
the  attack  of  insects  on  the  hides.  It  is  used  extensively  in  taxi- 
dermy, where  the  skins  of  fish,  of  beasts  and  birds  are  subjected 
to  a  thorough  rubbing  with  white  arsenic  before  mounting.  It 
is  used  also  in  the  preservation  of  moths,  butterflies  and 
larvae. 


170  ECONOMIC  GEOLOGY 

Arsenic  is  used  in  the  manufacture  of  glass,  in  the  manufacture 
of  certain  alloys.  Perhaps  the  most  important  of  these  is  shot. 
The  presence  of  1  per  cent,  of  arsenic  renders  the  lead  more 
fluid  when  heated,  therefore,  it  more  readily  assumes  the  spherical 
form  when  dropped  from  the  shot  tower.  The  alloy  upon  solidi- 
fication is  much  harder  than  pure  lead,  therefore,  it  has  greater 
penetrating  power.  Its  greater  rotundity  imparts  swiftness  and 
accuracy. 

Arsenic  with  many  metals  renders  them  both  hard  and  brittle. 
This  is  especially  true  of  tin.  When  only  a  few  thousandths  of 
1  per  cent,  of  arsenic  is  present  it  renders  both  gold  and  silver 
brittle.  Arsenic  also  hardens  copper  and  renders  it  brittle.  It 
is  an  injurious  constituent  of  brass.  Brass  with  0.5  per  cent,  of 
arsenic  cracks,  breaks  down,  and  will  not  roll.  In  fact  it  has 
refused  to  roll  .with  0.02  per  cent,  present.  It  increases  the 
fluidity  of  brass,  and  with  less  than  0.02  per  cent,  decreases  its 
ductility.  Arsenical  bronzes  contain  from  8  to  10  per  cent,  of 
arsenic.  It  is  evident,  therefore,  that  white  arsenic  comprises  by 
far  the  larger  part  of  the  arsenic  of  commerce.  If  other  forms 
are  required  as  in  the  manufacture  of  colors,  or  in  the  various 
medicinal  preparations  the  refined  forms  or  the  arsenical  prepara- 
tions are  manufactured  by  those  parties  most  concerned  in  their 
industrial  application. 

It  is  often  stated  that  the  arsenic  industry  is  fraught  with  great 
danger  of  blood  poisoning,  and  other  evils  to  the  employee. 
This  appears  to  be  an  exaggeration.  True  it  is  that  some  opera- 
tions can  be  conducted  only  by  skilled  workmen,  who  know  what 
precautions  have  to  be  taken  and  how  to  take  them.  All  work 
demands  care,  but  especially  where  there  is  dust,  as  in  the  clean- 
ing out  of  chambers,  in  grinding  the  white  arsenic,  and  in  filling  the 
barrels.  In  these  dusty  operations  the  nostrils  are  kept  plugged 
with  cotton  wool,  and  in  cleaning  out  the  flues  the  limbs  are  kept 
bandaged.  In  Cornwall  and  Devon,  England,  where  these  pre- 
cautions are  observed  arsenical  poisoning  is  rare. 

Among  the  new  industries  that  have  recently  been  developed  in 
the  United  States  is  the  manufacture  of  white  arsenic  by  the 
Puget  Sound  Reduction  Company  at  Seattle,  Washington.  The 
Company  recovers  the  arsenic  from  the  Monte  Cristo,  Washing- 
ton ores.  In  1907  a  company  was  incorporated  at  Carmel,  Put- 
nam County,  New  York,  for  mining,  concentrating  and  exporting 
arsenopyrite. 


USEFUL  METALS  171 

Antimony :  Its  Properties,  Occurrences  and  Uses 

Properties. — Antimony,  symbol  Sb,  is  a  tin  white,  extremely 
brittle  metal.  It  is  distinguished  from  all  other  metals,  save  bis- 
muth, by  its  brittleness  and  from  all  the  other  metals  in  the  char- 
acter of  its  salts.  In  many  respects  these  are  more  closely  allied 
to  the  salts  of  the  metalloid  arsenic  than  to  those  of  the  true 
metals.  It  fuses  easily  before  the  blow  pipe  forming  dense  white 
fumes  of  the  white  oxide,  Sb203.  If  heated  intermittently  there 
appears  upon  the  button  prismatic  crystals  of  artificial  valen- 
tinite.  The  metal  does  not  tarnish  at  the  ordinary  temperatures. 
It  is  soluble  in  concentrated  HC1;  specific  gravity,  6.7,  melting 
point,  630.5°  C.,  and  its  atomic  weight  is  120.2. 

Ores  of  Antimony. — Native  antimony,  Sb,  100  per  cent.  Sb. 
Often  alloyed  with  silver,  arsenic  and  iron. 

Stibnite,  Sb2S3,  71.4  per  cent.  Sb.  Massive  or  in  reticulated 
crystals. 

Kermesite,  2Sb2S3,Sb203,  75  per  cent.  Sb.  A  cherry-red  pris- 
matic mineral. 

Valentinite,  Sb203,  83.3  per  cent.  Sb.  Occurring  in  white  or- 
thorhombic  crystals. 

Senarmontite,  Sb203,  83.3  per  cent.  Sb.  Occurring  in  white  iso- 
metric crystals. 

Cervantite,  Sb203,Sb205,  78.9  per  cent.  Sb.  Yellow  or  yellowish- 
white  in  color. 

Antimony  occurs  also  with  many  lead  ores  as  galenite.  From 
this  mineral  the  extraction  of  the  antimony  is  somewhat  difficult. 
It  occurs  also  with  several  silver  ores.  It  is  also  associated  with 
some  gold  ores. 

Origin  of  the  Ores. — Native  antimony  is  derived  from  the 
reduction  of  the  other  ores  of  the  metal.  Stibnite  is  slightly  sol- 
uble in  water  at  80°  C.,  and  its  recrystallization  from  such  a 
solution  is  perceptible.  Stibnite  has  been  reported  from  Tuscany 
as  a  product  of  solfataric  action.  According  to  F.  W.  Clarke,  this 
mode  of  deposition  is  ascribed  to  the  fact  that  the  metal  forms 
easily  volatile  compounds.  In  most  cases  stibnite  has  been  de- 
posited from  alkaline  solutions  which  have  the  power  to  dissolve 
silica.  In  this  manner  solutions  bearing  antimony  may  be  trans- 
ported a  considerable  distance  from  the  original  ore  body.  The 
same  alkaline  solutions  have  the  power  to  dissolve  silica,  and  this 
explains  the  presence  of  quartz  as  the  most  important  gangue 
mineral  for  stibnite. 


172  ECONOMIC  GEOLOGY 

According  to  J.  D.  Dana,  the  amorphous  brick  red  mineral 
metastibnite,  Sb2S3,  occurs  with  cinnabar  deposited  upon  siliceous 
sinter  at  Steamboat  Springs,  Nevada. 

The  oxysulphide  results  directly  from  a  partial  oxidation  of 
stibnite.  Valentinite  and  senarmontite  are  oxidation  products  of 
other  ores  of  antimony.  Valentinite  crystallizes  from  solu- 
tions above  100°  C.  and  senarmontite  solidifies  at  the  lower 
temperatures. 

Character  of  the  Ore  Bodies. — Antimony  ores  occur  most 
abundantly  in  fissure  veins  traversing  both  the  igneous  and  the 
sedimentary  rocks.  They  occur  also  in  flats,  pitches,  and  as  im- 
pregnation deposits.  The  gangue  minerals  in  the  order  of  their 
importance  are  quartz,  calcite  and  barite.  The  associated 
minerals  are  the  gold  and  silver  ores,  cinnabar,  galenite  and 
sphalerite. 

Geographical  Distribution.— In  the  United  States  small  quan- 
tities of  antimony  ores  are  found  in  the  Appalachian  belt  but  none 
of  the  occurrences  appear  to  be  of  commercial  significance. 
These  small  deposits  may  be  observed  at  Soldier's  Delight,  Mary- 
land ;  Lyme,  New  Hampshire. ;  and  Carmel,  Maine.  In  southeast- 
ern Arkansas  stibnite  occurs  in  bedded  veins  traversing  Carbonifer- 
ous limestones  and  shales.  In  Idaho  auriferous  antimony  ores  oc- 
cur in  flats  and  pitches  near  Burke,  Shoshone  County.  The  gold 
content  is  reported  as  $20  per  ton  of  ore.  In  Nevada,  which  has 
been  an  important  producer,  exceptionally  pure  stibnite  occurs 
with  little  gangue  mineral  near  Austin  in  well-defined  contact 
fissures  between  shale  which  forms  the  foot  wall  and  calcareous 
sandstones  and  lime  porphyries.  In  Utah  it  is  disseminated 
through  conglomerates  and  sandstone  along  the  planes  of  strati- 
fication. In  California  stibnite  occurs  in  well-defined  fissure  veins 
with  a  quartz  gangue. 

In  York  County,  New  Brunswick,  auriferous  and  argentiferous 
native  antimony  and  stibnite  are  found  in  fissure  veins  with  quartz 
and  calcite  gangues  traversing  black  slates. 

According  to  Thomas  and  MacAlister,  the  Algerian  deposits 
occur  in  the  Province  of  Constantine  in  the  neighborhood  of  Jebel 
Hammamet.  The  ore,  which  exists  chiefly  as  oxide,  is  found  in 
irregular  layers  running  parallel  to  the  beds  of  black  limestone  of 
Lower  Carboniferous  age  with  which  it  is  associated.  These  ores 
were  at  one  time  considered  as  simple  sedimentaries,  deposited 
contemporaneously  with  the  enclosing  limestones.  It  appears, 


USEFUL  METALS  173 

however,  that  metasomatic  replacement  of  the  limestone  more 
closely  approximates  to  the  true  explanation  of  the  facts  observed. 

According  to  K.  Yamada,  antimonial  ores  occur  on  the  island 
of  Shikoku  in  lodes  in  a  sericite  schist  with  quartz  as  the  chief 
gangue  mineral.  Magnificient  groups  of  splendent  crystals  of 
stibnite  that  have  found  their  way  into  many  museums  occur  in 
the  extensive  antimony  mines  in  the  Province  of  lyo  on  the  same 
island. 

In  the  order  of  their  importance,  Bolivia,  France,  Hungary 
and  Spain  are  the  commercial  producers  of  antimony. 

Geological  Horizon. — The  ores  of  antimony  are  not  confined 
to  any  particular  geological  horizon.  Those  in  the  Appalachian 
belt  are  associated  with  the  older  crystalline  schists.  Those  in 
Arkansas  occur  in  the  Carboniferous.  In  Tuscany  antimony 
lodes  occur  between  the  Permian  shales  and  the  Eocene  lime- 
stones. 

Methods  of  Extraction.  (1)  Roasting. — Owing  to  the  low 
fusion  point  of  stibnite,  melting  easily  in  a  candle  flame,  the  ore 
is  crushed  and  roasted,  the  liquated  sulphide  drawn  off  in  in- 
clined iron  pipes.  The  sulphide  is  then  roasted  in  a  current  of 
air  when  the  oxide,  Sb2O3,  is  formed.  The  oxide  is  then  re- 
duced to  the  metallic  state  by  common  salt  or  scrap  iron.  The 
crude  metal  thus  obtained  is  further  refined  by  roasting  with 
scrap  iron.  The  following  reaction  may  obtain,  Sb2S3+3Fe  = 
3FeS+Sb2.  The  process  is  applicable  to  the  sulphides  of  the 
metal. 

(2)  The  Crucible  Method. — Native   antimony  is  crushed   and 
heated  in  large  graphite  crucibles  with  scrap  iron.     If  any  sul- 
phur is  present  it  unites  with  the  iron  in  the  formation  of  the 
sulphide  of  iron  as  represented  in  the  above  equation.     The 
antimony  by  its  higher  specific  gravity  sinks  to  the  bottom  of 
the  crucible  as  a  bluish-white  crystalline  metal.     The  process  is 
applicable  to  the  native  metal  and  to  the  sulphide,  stibnite. 

(3)  The  Wet  Method. — Stibnite  is  dissolved  in  hot  concentrated 
HC1  and  precipitated  from  its  solution  by  iron  or  zinc.     It  may 
also  be  precipitated  by  pouring  into  water  when  the  oxychloride, 
SbOCl  is  formed. 

(4)  The  Reduction  Process. — The  oxides  of  antimony,  valentinite 
and  senarmontite,  may  be  reduced  to  the  elemental  state  by 
reduction  with  carbon. 


174  ECONOMIC  GEOLOGY 

(5)  Electrolytic  Method. — The  electrolytic  process  may  also 
be  utilized  in  the  production  of  metallic  antimony.  The  process 
of  refining  metallic  antimony  is  very  difficult  and  few  understand 
the  details  of  modern  practice  in  the  industry. 

Uses  of  Antimony. — Antimony  is  used  extensively  in  alloys. 
In  general  a  mixture  of  antimony  with  other  metals  renders 
them  more  lustrous,  hard,  and  somewhat  brittle.  The  alloys 
of  antimony,  like  those  of  bismuth,  expand  upon  cooling,  there- 
fore they  make  fine,  hard,  sharp  castings.  An  alloy  consisting 
of  86.5  per  cent,  lead  and  13.5  per  cent,  antimony  is  4  times 
as  hard  as  pure  lead.  An  alloy  consisting  of  35.86  per  cent, 
lead  and  64.14  per  cent,  antimony  is  11.7  times  as  hard  as  pure 
lead. 

Type  metal  consists  of  lead,  antimony,  and  often  tin  in  vary- 
ing proportions.  Ten  varieties  of  type  metal  are  well  known. 
The  first  of  the  series  consists  of  75  parts  lead  and  25  parts 
antimony;  another  of  75  parts  lead,  20  parts  antimony,  and  5 
parts  tin.  Type  metal  must  cast  readily  and  be  capable  of  tak- 
ing sharp  impressions.  It  must  be  hard  enough  to  resist  crush- 
ing in  the  press  and  so  soft  that  its  edges  will  not  cut  the  paper  in 
the  process  of  printing. 

Stereotype  metal  consists  of  112  parts  lead,  18  parts  antimony, 
and  3  parts  of  tin;  britannia  metal,  140  parts  tin,  9  parts  anti- 
mony, and  3  parts  copper;  pewter  89.3  per  cent,  tin,  7.1  per  cent, 
antimony,  1.8  per  cent,  copper,  and  1.8  per  cent,  bismuth; 
argentite  85.5  per  cent,  tin  and  14.5  per  cent,  antimony;  the 
luster  of  the  latter  alloy  so  closely  resembles  silver  that  it  is 
sometimes  difficult  to  distinguish  the  white  metal  from  the 
alloy  that  carries  no  silver.  This  alloy  is  used  extensively  in  the 
silver  ware  of  commerce. 

Babbitt  is  the  name  applied  to  a  wide  series  of  antifriction  alloys 
used  extensively  in  the  journals  of  cars,  locomotives,  and  other 
rapidly  moving  machinery.  It  consists  of  antimony,  tin  and 
copper,  with  small  amounts  of  lead,  zinc,  bismuth  and  nickel. 
The  tin  always  exceeds  50  per  cent,  and  the  copper  may  be 
entirely  replaced  by  antimony,  or  the  antimony  by  copper. 

Antimony  alloys  with  aluminum  in  all  proportions  at  a  com- 
paratively low  temperature.  With  less  than  5  per  cent,  of  anti- 
mony the  alloy  is  vastly  superior  to  aluminum  in  hardness,  te- 
nacity, elasticity,  and  malleability.  It  is  more  sonorous  when 
struck.  It  resists  the  corrosive  action  of  the  gases  of  the  at- 


USEFUL  METALS  175 

mosphere  better  than  many  other  alloys,  or  the  pure  metals 
themselves.  If  the  proportion  of  antimony  is  increased  the 
alloy  is  proportionately  harder,  but  correspondingly  weaker  in 
tenacity  and  elasticity.  If  the  antimony  exceeds  10  per  cent, 
the  alloy  crystallizes  in  beautiful  laminae.  Both  the  melting 
point  and  the  ease  of  corrosion  increases  with  the  antimony  and 
strikes  a  maximum  at  the  true  aluminum  antimonide,  Al2Sb2. 
Its  melting  point  is  higher  than  that  of  steel  but  the  melting 
point  of  its  constituents  is  very  low.  It  is  not  attacked  by  dry 
air  at  the  ordinary  temperatures,  but  at  the  higher  temperatures 
it  is  oxidized.  Under  the  influence  of  moist  air  at  high  tempera- 
tures the  alloy  is  readily  decomposed.  If  the  per  cent,  of  anti- 
mony be  still  further  increased  both  the  melting  point  and  the 
corrodability  of  the  alloy  are  proportionately  decreased.  The 
antimony  aluminum  alloy  readily  combines  with  other  metals 
forming  a  complex  series,  some  of  which  are  susceptible  of  a  high 
polish  and  capable  of  industrial  application.  The  aluminum, 
nickel  and  antimony  alloys  and  the  tungsten,  silver  and  antimony 
alloy  are  exceedingly  important  and  remarkable  for  their  intense 
hardness,  tenacity  and  elasticity.  The  alloys  of  antimony  with 
silver,  aluminum,  nickel  and  copper  are  susceptible  of  a  high 
polish  and  capable  of  wide  industrial  application.  The  alloys  of 
antimony  with  iron  and  steel,  with  or  without  nickel  and  chro- 
mium, are  extremely  fine  grained,  absolutely  free  from  flaws, 
hard  and  tenacious.  With  copper  alone  1  part  of  antimony 
in  1000  parts  of  the  red  metal  will  destroy  all  of  its  beneficent 
effects.  With  copper,  it  is  one  of  the  most  dreaded  of  all  impuri- 
ties as  it  occasions  cracks  in  the  rolling  of  the  metal.  It  also  is  ah 
injurious  constituent  in  the  brasses  and  bronzes. 

Antimonial  lead  or  hard  lead  is  an  alloy  of  the  two  metals 
indirectly  derived  from  the  treatment  of  antimonial  gold  and 
silver  ores.  For  antimonial  lead  there  is  a  good  demand.  Much 
antimony  in  commercial  tin,  zinc,  arsenic,  and  copper  reaches 
the  market  as  a  by-product  in  the  metallurgy  of  base  bullion 
and  is  sold  direct  as  an  alloy. 

Antimony  is  used  in  dying  as  a  mordant  for  vegetable  colors. 
It  is  used  also  in  medicine.  The  most  common  form  is  known 
in  commerce  as  tartar  emetic,  a  tartrate  of  antimony  and  'potas- 
sium. It  has  caused  death  when  applied  to  the  skin  as  a  local 
irritant  or  vesicant.  It  has  a  nauseous  and  metallic  taste. 
The  sulphide,  Sb2Sa,  has  also  been  used  in  medicine.  It  is  also 


176  ECONOMIC  GEOLOGY 

used  as  a  pigment.  The  crude  ore  was  crushed  and  used  by  the 
ancients  for  coloring  the  hair,  eyebrows,  eye  lashes  so  as  to 
increase  the  apparent  size  of  the  eyes. 

Antimony  plays  an  important  part  in  the  refining  of  gold. 
It  is  also  used  in  the  manufacture  of  matches  and  percussion  caps. 
Antimony  pentasulphide  is  a  bright  red  pigment  used  in  the  manu- 
facture of  vulcanized  rubber  and  in  many  forms  of  fireworks. 
Antimony  trisulphide  is  a  fiery  red  pigment  used  in  certain  paints. 
Antimony  is  used  in  the  lining  of  lead  chambers  for  the  manu- 
facture of  sulphuric  acid.  It  is  also  used  in  the  manufacture  of 
toys  and  in  coffin  trimmings.  The  soluble  salts  of  antimony  are 
powerful  irritant  poisons,  and  0.092  of  a  gram  has  proven  fatal. 

Economics. — Antimony  for  the  consumption  in  the  United 
States  is  largely  derived  from  four  sources.  (1)  Hard  lead  ob- 
tained in  the  smelting  of  foreign  and  domestic  ores;  (2)  imported 
regulus  or  metal;  (3)  imported  antimony  ores,  and  (4)  domestic 
ores.  Considerable  quantities  of  antimony  are  also  recovered 
from  the  drosses  of  old  type  metal  and  similar  sources  by  firms 
making  a  speciality  of  this  branch  of  metallurgy. 

The  reasons  for  the  small  production  of  antimony  in  the  United 
States  are:  (1)  The  low  price  of  the  metal;  (2)  the  low  cost  of 
production  in  foreign  countries;  (3)  the  distance  of  known  Amer- 
ican deposits  from  market;  (4)  extensive  foreign  deposits;  (5) 
the  difficulty  in  smelting  the  ores;  (6)  low  ocean  freight  rates, 
and  (7)  the  low  duty  on  crude  antimony. 

Tin:  Its  Properties,  Occurrence  and  Uses 

Properties. — Tin,  symbol  Sn,  is  a  white  metal  remaining  untar- 
nished in  either  dry  or  moist  atmosphere.  It  is  soft  enough  to 
cut  with  a  knife,  malleable  enough  to  be  beaten  out  into  a  leaf, 
and  ductile  enough  to  be  drawn  out  into  a  fine  wire.  At  a  tem- 
perature a  little  below  its  melting-point  it  becomes  brittle  and  can 
be  powdered.  The  "tin  cry"  is  emitted  whenever  the  metal  is 
bent.  No  other  metal  cries  so  distinctly.  It  results  from  the 
friction  of  .the  crystalline  particles  moving  upon  each  other.  This 
friction  perceptibly  evolves  heat.  Tin  is  insoluble  in  the 
strongest  nitric  acid,  but  ordinary  concentrated  nitric  acid  oxi- 
dizes tin  to  metastanic  acid,  H^SnQa.  The  metal  is  readily  sol- 
uble in  concentrated  HC1.  Its  specific  gravity  is  7.3,  melting 
point,  232°  C.,  and  its  atomic  weight,  119. 


USEFUL  METALS  177 

Ores  of  the  Metal. — Native  tin,  Sn,  100  per  cent.  Sn.  Often 
with  gold  copper,  platinum  and  iridosmine. 

Stannite,  Cu2S,FeS,SnS2,  27  per  cent.  Sn.  Sometimes  known 
as  "bell  metal,"  on  account  of  its  bronze  color. 

Cassiterite,  Sn02,  78.67  per  cent.  Sn.  The  most  important 
ore. 

There  are  also  a  few  rare  tin  minerals.  Of  these  nordenskiol- 
dine,  a  borate  of  calcium  and  tin,  CaO,  SnO2,  B2Os,  is  the  most 
interesting  from  a  mineralogical  point  of  view  for  it  connects  tin 
with  the  important  mineralizer  boron. 

Several  varieties  of  cassiterite  are  known.  If  it  occurs  in 
crystals  or  in  masses  it  is  known  as  tin  stone.  If  in  forms  radia- 
ting and  fibrous  closely  resembling  wood,  it  is  called  wood 
tin.  If  in  warty  aggregations  it  is  called  toad's  eye  tin.  If  in 
rounded  grains  of  sand  along  the  beds  of  streams  it  is  known  as 
stream  or  placer  tin. 

Origin  of  the  Ores. — Native  tin  which  is  very  rare  occurs  only 
in  small  quantities  perhaps  as  a  decomposition  and  reduction 
product  of  other  tin  minerals.  It  occurs  in  grains  in  New  South 
Wales  but  its  occurrence  with  gold  in  Siberia,  in  Bolivia,  and  at 
Guanajuato,  Mexico,  are  all  doubtful.  The  native  tin  reported 
from  Bolivia  is  believed  to  be  artificial. 

The  association  of  stannite  in  Cornwall,  England,  with  pyrite 
and  sphalerite,  together  with  the  occurrence  of  stannite  at  Zin- 
wald  in  the  Erzgebirge  with  sphalerite  and  galenite  would  imply 
the  deposition  of  the  minerals  from  solution.  This  sulphide  so 
pronouncedly  suggesting  in  its  appearance  varieties  of  " bronze" 
or  "bell  metal"  is  called  by  the  miners  bell-metal  oreJ 

Cassiterite  is  by  far  the  most  important  source  of  the  tin  of 
commerce.  It  is  both  primary  and  secondary  in  its  origin. 
According  to  F.  W.  Clarke,  it  has  been  repeatedly  observed  as  a 
furnace  product  formed  by  the  direct  oxidation  of  tin.  Accord- 
ing to  C.  Doelter,  cassiterite  is  perceptibly  soluble  in  water  at  a 
temperature  of  80°,  but  more  soluble  in  the  presence  of 
sodium  fluoride.  He  also  observed  some  crystallization  from 
such  solutions.  S.  Meunier  found  0.5  per  cent,  of  cassiterite  in  an 
opaline  deposit  somewhat  resembling  geyserite,  from  a  thermal 
spring  in  Selangor.  J.  H.  Collins  reports  cassiterite  as  a  cement 
in  certain  Cornish  conglomerates,  also  as  impregnation  deposits 
in  long  buried  horns  of  deer,  as  pseudomorphs  after  feldspar, 
as  cappings  on  crystals  of  quartz,  as  fissure  linings  in  quartz,  as 
12 


178 


ECONOMIC  GEOLOGY 


an  incrustation  on  an  ingot  of  ancient  tin,  as  a  secondary  crystal- 
lization on  reniform  masses  of  wood  tin.  F.  W.  Clarke  regards 
all  these  as  evidences  or  proof  that  the  famous  Cornish  ores  are  of 
aqueous  origin. 

According  to  F.  A.  Genth,  pseudomorphs  of  cassiterite  after 
hematite  occur  at  Durango,  Mexico.  W.  Semmons  has  also 
described  the  presence  of  cassiterite  as  a  concentric  coating  on 
bismuthinite. 

According  to  Thomas  and  MacAlister,  cassiterite  occurs  as  an 
original  constituent  of  a  few  granites  and  acid  volcanic  rocks 
diffused  more  or  less  uniformly  through  the  rock  mass,  but  par- 


FIG.  98. — Vein  of  Cassiterite,  quartz  and  tourmaline,  traversing  Paleozoic 
slates  which  consist  of  alternate  bands  of  siliceous  and  argillaceous  materials, 
Belowda  Beacon,  Cornwall,  England.  (After  Thomas  and  MacAlister's 
Geology  of  Ore  Deposits.) 


ticular  as  inclusions  in  mica.  Such  primary  segregations  they 
regard  as  insufficiently  large  to  be  of  direct  economic  value,  but 
they  may  ultimately  yield  rich  alluvial  deposits. 

The  detrital  deposits  bearing  tin  are  derived  from  the  disinte- 
gration and  wearing  away  of  the  acid  intrusives  and  contact 
metamorphic  rocks  in  which  the  tin  lode  occurs,  and  its  presence 
in  the  placer  gravels  at  no  considerable  distance  from  its  original 
home  to  the  transporting  and  sorting  power  of  water.  The  ores 
of  tin  appear  to  occur  as  primary  segregations,  as  pneumatolytic 
deposits,  as  metasomatic  replacement  deposits,  and  as  detrital 
deposits. 


USEFUL  METALS  179 

Character  of  the  Ore  Bodies. — Cassiterite  occurs  as  a  primary 
segregation  in  the  acid  intrusives.  It  is  found  in  fissure  veins 
traversing  granites,  pegmatites,  gneisses,  porphyries,  mica  schists, 
chlorite  schists,  etc.  Its  home  is  often  in  veins  of  pegmatite 
associated  with  lithium  bearing  minerals  as  tourmaline,  lepidolite, 
zinnwaldite  and  spodumene.  This  type  of  formation  is  pro- 
nounced in  Maine,  the  Carolinas,  the  Black  Hills,  and  in  South 
Africa. 

The  second  type  of  formation  might  lead  to  the  conclusion  that 
cassiterite  is  a  product  of  secondary  deposition.  It  is  found  in 
veins,  beds,  and  stocks  in  association  with  quartzose,  crystalline 
schists,  and  even  traversing  shales.  (See  Fig.  98.)  Penrose  has 
reported  tin  in  the  Malay  Peninsula  as  occurring  in  beds  in  lime- 
stones and  sometimes  even  in  sandstones. 

The  most  important  mode  of  occurrence  is  in  quartz  veins 
traversing  granites  and  pegmatites.  The  granite  has  become 
greisenized,  that  is,  orthoclase  has  altered  to  lepidolite  and  zinn- 
waldite with  topaz  and  tourmaline  as  associated  minerals.  The 
presence  of  minerals  bearing  boron  and  fluorine,  together  with 
the  greisenization  of  the  granite  walls  would  lead  to  the  con- 
clusion that  cassiterite  may  be  formed  by  the  injection  of  vapors 
bearing  tin  and  the  well-known  mineralizers  fluorine  and  boron. 
Fluorine  is  able  at  a  high  temperature  to  form  a  volatile  compound 
with  tin,  which  at  lower  temperatures  and  in  the  presence  of 
steam  would  be  decomposed  into  the  oxide  of  tin  and  hydro- 
fluoric acid  according  to  the  following  equation,  SnF4+2H2O  = 
Sn02+4HF. 

Geographical  Distribution. — There  are  five  distinct  belts  of 
tin-bearing  minerals  in  the  United  States,  but  none  of  them 
have  assumed  the  proportions  of  a  large  producer.  (1)  The 
Appalachian  belt;  (2)  the  Black  Hills  district;  (3)  the  Cordilleran 
section;  (4)  the  Pacific  Coast  belt,  and  (5)  the  Alaskan  district. 

(1)  The  Appalachian  Belt. — Numerous  deposits  of  cassiterite 
occur  in  this  belt  which  stretches  from  Alabama  to  Maine.  In 
Maine  tin  ores  occur  in  Hebron,  Paris,  Stoneham  and  Winslow. 
In  Massachusetts  cassiterite  occurs  in  Chesterfield  and  Goshen 
associated  with  albite  and  tourmaline.  In  Virginia  it  is  found  in 
Rockbridge  County  with  wolframite.  The  most  promising 
field  in  this  belt  lies  in  the  Carolinas.  According  to  L.  C. 
Graton  and  H.  Ries,  it  stretches  from  near  Gaffney,  Cherokee 
County,  South  Carolina,  across  parts  of  Cleveland  and  Gaston 


180 


ECONOMIC  GEOLOGY 


Counties,  North  Carolina,  to  Lincolnton,  a  distance  of  about  35 
miles.  The  ore  is  irregularly  distributed  in  pegmatite  dikes 
traversing  the  metamorphic  sedimentaries.  Both  the  acid  and 
the  basic  intrusives  are  present.  The  acid  intrusives  is  the  home 
of  the  cassiterite  (see  Fig.  99). 

(2)  The  Black  Hills  District. — This  field  represents  the  most 
important  occurrence  of  tin  ores  in  the  United  States  outside  of 
Alaska.  The  ore  is  of  three  types.  In  quartz  veins,  impregna- 
tion deposits,  and  in  placers.  The  last  results  in  the  normal 
disintegration  of  the  associated  tin-bearing  rocks  and  the  con- 


FIG.  99. — Sketch  map  showing  the  location  of  the  Carolina  tin  belt. 
After  Graton.  (By  permission  of  the  Macmillan  Company,  from  Ries1 
Economic  Geology.) 

centration  of  the  stream  tin  through  the  sorting  power  of  water. 
The  placers  carry  the  purest  tin  ores,  for  the  other  ores  of  lower 
tin  content  associated  with  the  lode  deposits  have  become 
oxidized  at  or  near  the  surface.  The  ore  occurs  with  wolframite 
and  scheelite. 

(3)  The  Cordilleran  Section. — A  few  reports  of  the  presence  of 
cassiterite  have  been  given  for  this  district  but  the  deposits  are 
not  large.     It  occurs,  however,  near  Dillon,  Montana,  and  in 
Crook  County,  Wyoming. 

(4)  The  Pacific  Coast  Belt. — The  Temescal  tin  mines  are  situ- 
ated near  the  northern  end  of  the  San  Jacinto  estate  in  San 


USEFUL  METALS  181 

Bernadino  County,  California.  The  principal  vein  varies  from 
a  few  inches  to  8  ft.  in  width.  In  1892  this  mine  was  a  producer 
of  pig  tin  and  bid  fair  to  be  of  considerable  commercial  impor- 
tance. It  has,  however,  since  that  date  been  only  a  small 
producer. 

(5)  The  Alaskan  Belt. — In  this  district  tin  occurs  in  lodes  and 
placers  in  the  Seward  Peninsula.  According  to  F.  L.  Hess,  the 
ores  occur:  (1)  In  quartz  veins  traversing  phyllite  schists;  (2) 
in  quartz  porphyry  dikes  traversing  limestones;  (3)  in  dis- 
seminations in  the  greisenized  granitic  rocks.  The  ores  are 
associated  with  calcite,  fluorite  and  the  lithium  mica,  zinnwaldite. 
A.  H.  Fay,  (Trans.  A.  I.  M.  E.,  1907)  mentions  one  deposit  as  a 
contact  between  limestone  and  granite  associated  with  much 
tourmaline.  This  area  bids  fair  to  be  of  some  commercial 
significance. 

Foreign  Countries. — Two  foreign  deposits  of  tin  ores  are  worthy 
of  special  consideration  for  they  have  been  the  largest  producers 
of  this  useful  metal.  The  first  of  these  is  Cornwall  and  Devon, 
England.  The  second  is  found  in  the  Federated  Malay  States. 

According  to  Thomas  and  MacAlister,  the  tin  deposits  in  the 
former  district  are  intimately  associated  with  five  large  granite 
batholiths.  Two  of  these  at  West  Cornwall,  England,  are 
intruded  in  sediments  of  Ordovician  age.  Two  in  central  and 
east  Cornwall,  in  rocks  of  Devonian  age.  One  in  Devonshire 
in  terranes  of  both  Devonian  and  Carboniferous  age. 

The  association 'of  tin  and  copper  ores  are  better  illustrated  at 
Cornwall,  England,  than  in  any  other  locality.  The  association 
of  the  tungsten  and  arsenic  minerals  with  those  of  copper  and  tin 
is  such  that  it  leads  to  the  conclusion  on  the  part  of  some  that  the 
ores  are  of  identical  age. 

The  cassiterite  poitions  of  the  lodes,  however,  occur  in  the 
older  parts  of  the  veins  and  appear  to  have  been  the  first  min- 
erals formed.  In  other  cases  the  cassiterite,  chalcopyrite,  ar- 
senopyrite  and  wolframite  are  so  intimately  associated  that  it 
renders  successive  deposition  a  matter  of  doubt  (Fig.  100). 

The  most  important  tin  deposits  of  the  world  are  found  in  the 
Federated  Malay  States.  The  leading  states  in  production  are 
Selangor,  Perak,  and  Pahang.  According  to  the  State  Geologist, 
Scrivenor,  the  origin  of  the  tin  lodes  and  their  association  with 
greisenized  granite  is  akin  to  those  in  England.  However,  much 
of  the  tin  mined  is  found  in  placers.  The  Kinta  Valley  is  one 


182 


ECONOMIC  GEOLOGY 


of  the  most  important  fields.  This  valley  is  about  40  miles  in 
length,  and  averages  about  15  miles  in  width.  The  amount  of 
tin  in  some  deposits  is  sometimes  20  per  cent.  The  tin-bearing 


alluvium  is   called  karang.     This  material  is  often   cemented 
together  by  limonite. 

The  kong  is  the  term  applied  to  materials  having  two  modes  of 


USEFUL  METALS  183 

origin.  In  one  case  it  implies  the  kaolinized  pegmatites  bearing 
some  quartz.  In  the  other  it  signifies  a  true  detrital  deposit. 
In  Parak  there  occurs  the  Lahat  pipe  which  consists  of  an  irregu- 
lar pipe-like  body  of  cassiterite  extending  to  a  depth  of  several 
hundred  feet.  The  pipe  was  originally  a  tin-bearing  vein  but 
subsequently  became  a  course  for  surface  waters.  The  adjacent 
limestone  was  taken  into  solution  and  transported  elsewhere. 
The  cassiterite  fell  into  this  solution  cavity  and  was  subsequently 
cemented  into  a  somewhat  brecciated  mass. 

According  to  Scrivenor,  the  detrital  cassiterite  deposits  on 
the  islands  of  Banka  and  Billiton  occur  in  two  different  ways. 
In  one  case  the  tin  is  found  on  the  hillsides  and  plains  not  far  from 


FIG.  101. — Reduction  works  of  the  Llallagua  tin  mine  in  Bolivia. 

the  lodes  from  which  it  was  derived.  In  the  other  it  is  found  in 
true  valley  detrital  material  which  sometimes  reach  a  depth  of 
50  ft.  The  tin-bearing  portion  of  the  placer  lies  in  the  lower  3  ft. 
of  the  deposit  and  is  associated  with  topaz  and  tungsten  minerals. 

More  than  half  of  the  world's  supply  of  tin  has  been  derived 
from  the  Federated  Malay  States  and  the  islands  of  Banka  and 
Billiton  off  Sumatra.  The  detrital  deposits  have  been  larger 
producers  than  the  lodes. 

A  third  foreign  area  of  somewhat  less  importance  is  found  in 
Bolivia.  The  deposits  are  of  special  interest  because  the  ores 
are  associated  with  lead,  silver  and  bismuth  minerals  in  a  dacite 


184  ECONOMIC  GEOLOGY 

and  trachite  of  recent  volcanic  origin.  It  is  supposed  to  be  of 
pneumatolytic  origin  and  to  provide  an  example  of  an  inter- 
mediate type  of  veins  between  well-known  tin  veins  with  greisen- 
ized  walls  and  the  true  veins  of  galenite  with  their  associated 
sulphides  (Fig.  101.) 

Geological  Horizon  of  Tin. — The  ores  of  tin  appear  to  be  asso- 
ciated with  the  early  as  well  as  the  late  intrusives  and  to  a  limited 
extent  with  the  later  crystalline  rocks. 

Methods  of  Extraction.  The  Smelting  Process. — Three  steps 
are  involved  in  the  process.  Calcining,  washing,  and  smelting. 
The  ore  is  crushed  and  washed  to  remove  all  earthy  materials. 
It  is  then  calcined  to  remove  any  volatile  constituents  that  may  be 
in  the  ore.  If  the  cassiterite  is  mixed  with  stannite,  the  sulphide 
of  tin,  copper  and  iron,  the  sulphur  passes  off  as  sulphur  dioxide. 
This  may  be  reduced  to  elemental  sulphur  and  sold  as  a  by-prod- 
uct or  converted  into  sulphurous  acid  which  is  so  extensively 
utilized  in  the  manufacture  of  paper  by  the  sulphite  process.  If 
the  ore  contains  arsenic  the  arsenic  is  conducted  into  the  condens- 
ing flues  of  the  reverberatory  furnace  where  it  is  deposited  as  the 
white  arsenic  of  commerce,  collected  and  sold  as  a  by-product. 
If  antimony  is  present  this  metal  will  also  be  converted  into  the 
oxide  which  may  be  collected  and  sold  as  a  by-product.  If 
tungsten  minerals  are  present  the  ore  is  treated  with  sodium 
carbonate  which  combines  with  the  tungsten  forming  sodium 
tungstate.  This  compound  is  also  sold  as  a  by-product.  In  the 
process  of  calcining  the  copper  is  converted  into  the  sulphate  and 
the  iron  into  its  oxide. 

The  second  step  in  the  process  is  washing.  This  removes  the 
copper  sulphate  as  a  solution  from  which  the  copper  may  be  re- 
claimed by  electrolysis.  It  also  washes  out  the  iron  oxides  and 
other  minerals  of  lower  specific  gravity  than  the  cassiterite.  The 
cassiterite  thus  concentrated  is  smelted  in  a  reverberatory  furnace 
with  carbon  or  powdered  charcoal  when  impure  metallic  tin  is  ob- 
tained according  to  the  equation,  SnO2+2C  =  Sn-f2CO. 

The  metal  now  more  or  less  alloyed  with  other  metals  is  re- 
melted,  to  separate  it  from  the  impurities.  The  molten  metal  is 
stirred  with  bits  of  green  wood  which  cause  a  separation  of  scum  or 
dross  from  the  metal.  The  reduced  metal  is  drawn  into  a  cast- 
iron  kettle,  ladeled  into  moulds,  and  the  blocks  thus  formed  are 
known  in  commerce  as  block  tin  or  pig  tin. 

In  the  process  for  the  manufacture  of  tin  as  carried  out  at  Corn- 


USEFUL  METALS  185 

wall,  England,  the  ore  is  mined,  hoisted  to  the  surface  (for  some 
of  these  mines  are  being  operated  at  a  depth  of  over  1,300  ft.), 
transported  to  the  stamp  mill  where  it  is  broken  down  by  hammers 
wielded  by  women,  crushed  in  the  stamp  mill  sufficiently  fine 
to  pass  through  a  40-mesh  sieve,  carried  by  water  to  the  dressing 
floor  where  it  is  concentrated  into  black  tin  consisting  of  about 
66  per  cent.  tin.  This  concentrated  product  is  either  sold  direct 
as  tin  ore  or  is  mixed  with  20  per  cent,  pulverized  charcoal  and 
smelted. 

Uses  of  Tin. — A  large  amount  of  tin  is  used  in  the  manufacture 
of  the  tinware  of  commerce.  The  object  to  be  plated  is  dipped  in 
a  bath  of  molten  tin.  The  interior  of  the  tin  is  a  sheet  of  iron  of 
varying  thickness.  The  exterior  of  the  tinware  is  a  thin  coat  or 
film  of  tin.  Between  the  two  there  is  a  thin  band  of  alloy  of  tin 
and  iron  which  serves  to  unite  the  two  metals.  When  the  surface 
of  the  iron  is  not  perfectly  smooth  protuberances  will  perforate 
the  tin  and  in  a  short  time,  through  the  oxidation  of  the  iron,  the 
dish  will  leak. 

Tin  is  used  extensively  in  the  manufacture  of  alloys.  Tin 
enters  into  combination  with  a  large  number  of  useful  metals 
forming  alloys  of  commercial  significance.  With  lead,  tin  will 
mix  in  all  proportions.  The  alloys  are  white  and  melt  at  a  tem- 
perature below  the  melting-point  of  tin.  One  of  the  most  im- 
portant of  these  is  known  as  solder  which  consists  of  varying 
proportions  of  tin  and  lead.  Common  solder  consists  of  1  part 
of  tin  and  one  of  lead.  Coarse  solder  of  1  part  of  tin  and  two 
of  lead.  Fine  solder  consists  of  2  parts  of  tin  and  one  of  lead. 

The  old  pewter  ware  which  has  become  so  highly  prized  for 
decorative  effect  in  many  dining  rooms  consists  of  3  parts 
of  tin  and  one  of  lead.  The  old  britannia  ware  consists  of  84 
parts  of  tin,  10  parts  of  antimony,  4  parts  of  copper,  and  2  parts  of 
bismuth.  Bell  metal  consists  of  20  parts  of  tin  and  80  parts  of 
copper. 

Tin  is  a  constituent  of  a  few  brasses  of  importance,  but,  strictly 
speaking,  brass  is  an  alloy  of  copper  and  zinc.  Tin  is  a  necessary 
constituent  of  all  bronzes.  Many  of  these  are  capable  of  wide  in- 
dustrial application.  It  is  also  a  requisite  constituent  in  speculum 
metal.  It  is  used  in  the  manufacture  of  naval  condensers.  It 
is  found  also  in  many  forms  of  babbitt.  The  true  babbitts 
carry  more  then  50  per  cent,  of  tin.  They  are  known  as  friction- 
bearing  alloys. 


186  ECONOMIC  GEOLOGY 

Tin  unites  with  mercury  in  the  formation  of  an  amalgam  used 
extensively  in  the  filling  of  teeth,  and  when  amalgamating  anew 
with  silver  as  a  cement  in  joining  the  teeth  together.  Tin  does 
not  readily  alloy  with  zinc  alone. 

Tin  is  used  also  in  the  detection  of  gold.  A  solution  of  stannous 
chloride  in  the  presence  of  stannic  chloride  or  free  chlorine  is  one 
of  the  most  delicate  tests  known  for  the  yellow  metal.  The  com- 
pound formed  whose  composition  has  been  somewhat  of  an  open 
question  is  known  as  the  purple  of  Cassius. 

An  interesting  point  appears  concerning  the  effect  of  tin  on 
canned  goods.  According  to  F.  Wirthle,  who  examined  a  large 
number  of  samples  of  canned  beef,  the  white  crust  sometimes 
formed  within  the  can  was  a  basic  tin  chloride  resulting  from  the 
action  of  the  salt  on  the  tin  surface  either  by  the  direct  action  of 
the  tin  or  by  freeing  first  some  organic  salts  of  the  tin,  which  was 
subsequently  converted  into  a  basic  sodium  stannous  chloride  and 
some  organic  sodium  salt.  From  a  large  number  of  determina- 
tions the  maximum  of  tin  obtained  was  0.014  per  cent,  in  a  can 
of  beef  that  was  five  years  old.  The  interior  of  the  can  was  cor- 
roded in  all  cases  where  tin  was  in  contact  with  fat,  and  not  in  a 
single  instance  had  corrosion  begun  where  tin  was  in  contact  with 
gelatin.  The  test  employed  in  the  detection  of  the  tin  was  a 
solution  of  stannous  chloride  and  ammonium  molybdate.  The 
test  is  delicate  to  21-5,000,000  part  of  tin  in  solution.  Even  with 
this  extreme  dilution  a  beautiful  blue  coloration  is  observed. 

There  have  been  three  sudden  advances  in  the  production  and 
consumption  of  tin.  The  first  came  in  the  fourteenth  century, 
which  was  marked  by  the  use  of  tin  for  bell  metal.  The  second 
came  in  the  eighteenth  century  which  was  marked  by  the  large 
use  of  tin  in  bronze  for  artillery.  The  third  comes  in  the  twen- 
tieth century  which  is  marked  by  a  large  consumption  of  tin  in 
canned  provisions. 

Tin  is  also  utilized  in  the  manufacture  of  tin  foil  for  wrapping 
many  small  articles  of  commerce.  The  foil  consists  of  a  very 
thin  sheet  of  lead  coated  with  a  thin  film  of  tin.  Tin  is  also  used 
in  silvering  mirrors  when  amalgamated  with  mercurjr.  The  chlo- 
ride of  tin  is  used  in  dying  and  printing.  The  artificial  oxide 
of  tin  under  the  name  of  putty  powder  is  used  in  polishing 
granite.  The  polish  thus  obtained  is  far  more  lasting  than  that 
produced  by  oxalic  acid. 

During  the  last  few  years  the  separation  of  tin  from  tin  plates, 


USEFUL  METALS  187 

scrap  tin,  type  metal,  babbitt,  friction-bearing  metals,  tin  cans, 
etc.,  has  been  carried  on  by  the  Vulcan  Metal  Refining  Company 
of  Sewaren,  New  Jersey.  The  method  of  extraction  is  by  elec- 
trolysis. Fifteen  per  cent,  of  tin  is  said  to  be  recovered  from  the 
old  scrap  tinware  at  a  very  low  expense.  The  residue  of  steel 
is  compressed  into  blocks  by  hydraulic  pressure  and  sold  to 
the  open-hearth  steel  manufacturers  for  the  same  price  as  scrap 
tin  (therefore  the  source  of  the  tinware  costs  nothing  save 
transportation). 

Several  companies  have  been  organized  in  the  United  States 
for  the  purpose  of  exploiting  tin  deposits  and  the  extraction 
of  the  metal  from  the  ores  obtained.  The  Niagara  Tin  Smelt- 
ing Company,  located  at  Niagara  Falls,  N.  Y.,  and  the  North 
American  Smelting  Company  of  North  Dakota.  These  compa- 
nies have  exploited  the  stream  deposits  in  the  Dakota  tin  belt 
and  sought  to  enter  actively  into  the  production  of  tin.  The 
American  Tin  Mining  Company  has  produced  a  few  tons  of 
placer  tin  from  Buck  Creek  in  the  Seward  Peninsula.  The 
Bartels  Tin  Mining  Company  in  1903  at  Tin  City,  5  miles  south- 
east of  Cape  Prince  of  Wales,  sunk  several  shafts  and  drove  many 
drifts  in  their  quest  for  tin,  but  the  results  were  meager.  The 
United  States-Alaska  Tin  Mining  Company  has  continued  pros- 
pecting by  tunnelling  to  a  vein  in  Cape  Mountain,  but  no  pro- 
duction has  resulted  from  their  labors.  The  Tinton  Company, 
South  Dakota,  has  remodeled  its  mill  and  expects  not  only  to 
mine  tin  but  reduce  the  ores  to  the  elemental  state. 

With  an  annual  importation  of  tin  valued  at  approximately 
$25,000,000  it  appears  as  though  the  active  exploitation  of  the 
tin  placers  and  lodes  deposits  in  the  possible  tin-bearing  belts  of 
the  Carolinas,  the  Black  Hills,  and  Alaska  should  be  reasonably 
rewarded  for  the  expenditure  of  time  and  money. 


CHAPTER  VII 
USEFUL  METALS  CONTINUED  (GROUP  III) 

IRON,  ALUMINUM,  CHROMIUM 
Iron :  Its  Properties,  Occurrence  and  Uses 

Properties. — Iron,  symbol  Fe,  is  a  lustrous  white  metal  sus- 
ceptible of  a  high  polish.  Native  iron  varies  in  color  from  steel 
gray  to  iron  black.  Iron  is  strongly  magnetic  but  loses  this 
property  when  highly  heated.  It  is  malleable  and  sectile.  It 
does  not  oxidize  in  dry  air  but  in  the  presence  of  moist  air  con- 
taining carbon  dioxide  it  becomes  coated  with  rust.  The  oxida- 
tion is  far  more  rapid  after  the  film  of  the  oxide  has  once  formed 
over  the  metal.  Iron  is  soluble  in  the  dilute  mineral  acids.  The 
metal  crystallizes  in  the  isometric  system.  The  specific  gravity 
of  native  iron  is  7.5,  while  that  of  the  furnace  product  is  8.1. 
Its  melting  point  is  between  1550°  and  1600°  C.  Its  atomic 
weight  is  55.85. 

Minerals  and  Ores. — Next  to  aluminum,  iron  is  the  most  abun- 
dant of  all  the  metals.  The  principal  iron  minerals  are  as  follows : 

Native  iron,  Fe,  100  per  cent.  Fe.  Often  alloyed  with  cobalt, 
nickel  and  copper. 

Pyrite,  FeS2,  46.6  per  cent.  Fe.  Commonly  known  as  fools 
gold,  crystallizes  in  cubes,  octahedrons  and  pyritohedrons. 

Marcasite,  FeS2,  46.6  per  cent.  Fe.  Occurs  in  orthorhombic 
crystals  radiating  from  a  common  center  and  in  an  aggregation 
of  crystals  flattened  into  a  crest-like  form  called  cocks-comb 
pyrite. 

Pyrrhotite,  FenSn+i.  With  plus  or  minus  61.6  per  cent.  Fe. 
Commonly  known  as  magnetic  pyrite. 

Melanterite,  FeSO4,7H20.     A  natural  green  vitriol. 

Coquimbite,  Fe2(SO4)3,9H2O.  A  ferric  sulphate  of  some  com- 
mercial significance  in  Chili. 

Siderite,  FeC03,  48.2  per  cent.  Fe.  Often  in  rhombohedrons 
with  curved  faces. 

188 


USEFUL  METALS  189 

Magnetite,  Fe304,  72.4  per  cent.  Fe.  The  only  iron-black 
mineral  strongly  magnetic  before  heating. 

Franklinite,  (Fe,Mn,Zn)0,(Fe,Mn)203,  44.1  per  cent.  Fe. 
Occurring  in  black  octahedrons  which  vary  in  the  degree  of  mag- 
netism and  in  the  per  cent,  of  iron  with  the  amount  of  manganese 
and  zinc  present. 

Hematite,  Fe203,  70  per  cent.  Fe.  The  only  mineral  with  cherry 
red  or  blood  red  streak.  It  includes  the  specular  iron  ore,  the 
Clinton  ore,  and  the  fossil  ore. 

Gothite,  Fe203,H20,  62.9  per  cent.  Fe. 

Xanthosiderite,  Fe203,2H20,  57.1  per  cent.  Fe. 

Turgite,  2Fe203,H20,  66.2  per  cent.  Fe. 

Limonite,  2Fe203,  3H20,  59.8  per  cent.  Fe. 

Of  the  last  species  named  only  one  of  them  appears  crystallized 
and  that  is  gothite.  They  are  all  classified  in  the  trade  as  limonite 
and  their  fine  powders  vary  in  color  from  reddish-brown  to  yellow. 
The  last  named  mineral,  limonite,  occurs  in  compact  forms, 
sometimes  in  a  pulverulent  state,  sometimes  in  stalactitic  forms, 
in  bog  ores,  and  as  brown  clay-iron  stone. 

There  are  also  many  arsenides,  arsenates,  chromates,  tungs- 
tates,  columbates,  niobates,  etc.,  of  iron  but  these  are  not  of 
sufficient  importance  as  a  source  of  iron  to  be  considered  here. 
In  fact,  the  minerals  of  which  iron  is  an  essential  constituent  are 
numbered  by  the  hundreds. 

The  iron  minerals  of  economic  significance  fall  distinctly  into 
four  classes: 

(1)  Those  used  for  the  extraction  of  the  metal.     These  in  the 
order  of  their  importance  in  America  are,  hematite,  limonite, 
magnetite,  and  siderite.     The  production  of  each  in  1905  was 
hematite  86.6;  limonite  8.8;  magnetite  4.5,  and  siderite  0.12  per 
cent,  of  the  total.     In  England  siderite  is  said  to  furnish  more 
than  50  per  cent,  of  the  pig  iron  of  Great  Britain. 

(2)  Those  used  in  their  natural  state  as  pigments  after  reduc- 
tion to  impalpable  powders;  hematite,  limonite,  and  to  a  limited 
extent  franklinite. 

(3)  Those  used  for  the  extraction  of  an  acid  radicle.     For  the 
extraction  of  sulphur  are:  pyrite,  marcasite,   and  pyrrhotite. 
For  arsenic  of  commerce:  lollingite,  FeAs2,  leucopyrite,  Fe3As4, 
and  arsenopyrite,  FeAsS.     For  the  extraction  of  chromic  acid: 
chromite,   FeO,Cr203.     For    the    extraction    of    tungstic    acid: 
wolframite,  (Fe;Mn)W04.     For  the  extraction  of  titanic  acid; 


190  ECONOMIC  GEOLOGY 

ilmenite,  FeO,Ti02.  The  last  three  are  used  in  the  manufacture 
of  chrome  steel,  tungsten  steel  and  titanium  steel. 

(4)  Those  used  in  the  extraction  of  an  included  metal.  For 
gold  and  silver;  pyrite,  marcasite,  and  pyrrhotite-.  For  nickel; 
pyrrhotite.  Practically  all  the  nickel  for  domestic  consumption 
in  the  United  States  comes  from  the  nickel-bearing  pyrrhotite 
deposits  of  Sudbury,  Ontario,  a  few  tons  of  nickel  only  being 
produced  at  Mine  La  Motte,  Missouri. 

The  sulphides,  arsenides,  and  phosphates  of  iron  play  no  part 
in  the  metallurgy  of  the  metal  in  America  because  of  the  deleteri- 
ous effect  of  each  upon  the  resulting  steel.  The  supply  of  the 
metal  comes  therefore  from  the  oxides,  the  hydrous  oxides  and 
the  carbonate. 

Origin  of  The  Ores  or  Minerals. — Native  iron  is  quite  widely 
distributed  as  a  primary  mineral  in  the  basic  intrusives  as  dia- 
base and  dolerite.  T.  Andrews  reports  native  iron  in  the  basalts 
of  Ireland.  F.  Navarro  found  the  metal  in  the  basalts  of  Gerona, 
Spain.  F.  F.  Hornstein  reports  native  iron  in  the  basalts  near 
Cassel,  Germany.  C.  H.  Cook  found  native  iron  in  the  trap 
rocks  of  New  Jersey.  According  to  G.  W.  Hawes,  native  iron 
occurs  in  the  dolerites  of  Dry  River  in  the  vicinity  of  Mount 
Washington.  The  iron  is  enclosed  in  grains  of  magnetite  which 
may  have  been  derived  as  a  secondary  mineral  from  the  native 
iron.  According  to  E.  Hussak,  native  iron  exists  in  the  Auriferous 
gravels  of  Brazil.  A.  Daubree  and  E.  Meunier  have  reported 
the  metal  from  the  gold  washings  in  the  Urals.  These  placers 
contained  traces  of  platinum  but  no  nickel. 

The  largest  and  the  most  important  body  of  native  iron  ever 
reported  was  discovered  by  A.  E.  Nordenskiold  in  1870  at  Ovifak, 
Disco  Island,  on  the  western  coast  of  Greenland.  Large  masses 
or  iron,  sometimes  weighing  20  tons,  are  encased  in  the  basalt  or 
weathered  out  in  boulder-like  or  lenticular  forms.  It  was  first 
reported  to  be  of  meteoric  origin.  Lieutenant  Peary  brought 
some  of  these  boulder-like  masses  of  iron  to  the  United  States, 
and  they  have  since  been  proven  to  be  of  terrestrial  origin. 

According  to  F.  W.  Clarke,  they  closely  resemble  meteoric  iron, 
for  they  responded  to  Widmannstatten  figures  when  etched,  con- 
tained the  rare  mineral  lawrenceite,  which  is  a  hydrous  ferrous 
chloride,  and  was  associated  with  magnetic  pyrite  and  graphite. 
Another  proof  of  its  terrestrial  origin  is  the  absence  of  schreiber- 
site,  the  phosphide  of  iron,  which  is  common  in  meteorites. 


USEFUL  METALS  191 

Strensthrup  found  native  iron  disseminated  in  large  bodies  of 
basalt  in  situ,  and. considered  it  a  part  of  the  rock  itself.  Two 
questions  have  arisen  concerning  its  origin :  (1)  Was  it  present  in 
the  original  magma  as  metallic  iron?  (2)  Was  it  reduced  by 
carbonaceous  matter  in  its  upward  transition  through  the  earths 
crust? 

F.  W.  Clarke  states  that  the  iron  may  have  come  as  such  from 
great  depths  below  the  surface  to  teach  us  that  the  earth  is  essen- 
tially a  vast  meteorite  and  that  its  interior  is  rich  in  uncombined 
metals. 

According  to  A.  Daubre*e  the  latter  supposition  is  admissable 
for  he  prepared  artificially  pellets  of  metallic  iron  containing 
nickel  almost  identical  in  composition  with  the  specimens  of 
native  iron  from  Disco  Island,  Greenland. 

According  to  C.  A.  Young,  from  20,000,000  to  24,000,000 
meteorites  fall  through  the  atmosphere  of  the  earth  every  24 
hours.  These  particles  blacken  the  snow  and  the  ice  of  the  perma- 
nent .snow  fields,  sink  to  the  bottom  of  the  ocean,  or  mingle  with 
the  soil  of  the  locality  in  which  they  happen  to  reach  the  earth. 

Troilite,  the  ferrous  sulphide,  FeS,  is  common  in  iron  meteor- 
ites in  nodules  disseminated  more  or  less  sparingly  through  the 
mass.  It  also  occurs  in  narrow  veins  usually  separated  from 
the  iron  by  a  thin  layer  of  graphite. 

Pyrite  and  pyrrhotite  occur  as  primary  minerals  as  minor  ac- 
cessories in  the  igneous  rocks.  The  former  appears  in  both  the 
acid  and  the  basic  intrusives,  while  pyrrhotite  is  more  character- 
istic of  the  ferromagnesian  varieties,  as  diabase  and  diorite. 
They  have  both  been  observed  as  sublimation  products  from 
volcanoes. 

According  to  F:  W.  Clarke,  dry  gases,  wet  gases,  and  alkaline 
solutions  charged  with  hydrogen  sulphide  are  capable  of  producing 
these  minerals.  The  magmas  contain  the  reagents  and  the  re- 
actions naturally  follow. 

According  to  J.  H.  L.  Vogt,  these  sulphides  are  actually  solu- 
ble in  silicate  magmas,  especially  at  high  temperatures,  and  are 
among  the  first  minerals  to  crystallize.  Vogt  regards  certain 
of  the  pyrrhotite  deposits  of  Norway  as  the  direct  product  of 
magmatic  segregation. 

Marcasite,  the  orthorhombic  sulphide,  FeS2,  is  common  in 
metalliferous  veins  and  in  the  sedimentary  rocks,  but  its  origin 
is  unknown. 


192  ECONOMIC  GEOLOGY 

The  nickeliferous  pyrrhotite  of  Sudbury,  Ontario,  is  by  some 
authorities  considered  to  represent  a  magmatic  segregation.  This 
origin  has  been  advocated  by  A.  P.  Coleman  and  others,  but 
the  more  recent  investigations  of  W.  Campbell  have  shown  that 
the  ores  were  deposited  from  circulating  solutions  and  therefore 
of  secondary  origin.  The  hydrous  sulphates  of  iron  are  always 
of  secondary  origin  and  of  minor  commercial  significance. 

Magnetite  is  often  a  primary  mineral,  solidifying  along  with 
chromite  as  the  first  segregations  of  a  periodotite  magma.  This 
origin  holds  especially  true  for  the  magnetites  and  chromates 
of  northern  Vermont  and  Megantic  County,  Quebec.  Magne- 
tite is  often  a  product  of  contact  metamorphism.  According  to 
C.  R.  Van  Hise,  magnetite  may  be  derived  from  marcasite  and 
pyrite  or  even  from  the  oxidation  of  siderite  in  situ.  The 
mineral  occurs  as  an  accessory  constituent  in  the  rocks  of  all 
classes,  but  it  is  obviously  more  abundant  in  the  rocks  rich  in 
the  ferromagnesian  minerals,  as  the  diabases  and  theperidotites. 
In  the  Lake  Superior  region  and  in  Michigan,  Minnesota  and 
Wisconsin,  magnetite  is  found  in  the  slates  and  cherts  where  the 
mineral  is  not  of  igneous  origin. 

According  to  C.  K.  Leith,  the  hematite  of  the  Mesabi  iron 
district  has  been  leached  from  a  hydrous  iron  silicate,  greenalite, 
as  FeO  and  developed  magnetite  where  oxidation  was  partial. 
Other  silicates  through  metamorphism  may  yield  magnetite. 

The  carbonate,  siderite,  is  always  of  secondary  origin.  It  may 
be  found  in  the  igneous  rocks  as  an  alteration  product.  Carbo- 
nated waters  can  extract  iron  from  silicate  rocks  or  disseminated 
hematite  and  deposit  their  load,  in  the  presence  of  much  car- 
bonic acid  or  decaying  organic  matter,  as  siderite.  If  the  air  has 
free  access  to  these  ferriferous  waters  the  hydrated  oxide,  limon- 
ite,  would  be  produced.  If  the  waters  are  muddy  the  silt  goes 
down  with  the  iron  compounds  and  the  clay  ironstones  are  the 
result.  The  black  band  ores  of  the  coal  measures  were  once  a 
carbonaceous  mud.  In  the  presence  of  reducing  agents  as  organic 
matter  the  carbonate  will  remain  as  such,  but  in  their  absence 
it  will  be  oxidized  and  limonite  may  be  the  resulting  product, 

According  to  F.  W.  Clarke,  hematite  can  crystallize  out  from  a 
magma  when  the  ferrous  compounds  are  either  absent  or  present 
in  quite  subordinate  amounts,  for  the  ferrous  oxide  unites  with 
it  to  form  magnetite.  Hematite  is  therefore  more  common  in 
the  acidic  than  in  the  basic  rocks.  It  is  found  as  a  pyrogenic 


USEFUL  METALS  193 

mineral  in  the  crystalline  schists  but  magnetite  is  far  more  abun- 
dant. According  to  C.  H.  Smyth,  Jr.,  the  oolitic  hematite  con- 
sists of  concentric  layers  of  hematite  deposited  around  grains 
of  quartz.  The  ore  was  formed  in  the  shoal  waters  of  a  Silurian 
sea,  presumably  upon  a  sandy  bottom.  The  iron  was  dissolved 
from  ferruginous  rocks  and  precipitated  from  solution  by  organic 
matter,  or  by  oxidation,  or  by  the  carbonate  of  lime.  The  Clinton 
ores  may  be  regarded  as  representing  a  contemporaneous  meta- 
somatic  deposit  in  which  the  ore  was  formed  during  or  imme- 
diately after  the  deposition  of  the  original  rock. 

Hematite  also  occurs  as  a  subsequent  metasomatic  ore  body. 
Here  the  replacement  took  place  some  time  after  the  deposition 
and  consolidation  of  the  original  rock.  The  ferric  sulphate 
traversing  limestones  may  have  the  iron  thrown  out  of  solution 
by  the  action  of  calcium  carbonate  as  hematite,  and  this  mineral 
will  then  be  deposited  along  the  walls  of  a  fault,  or  the  joint 
plains  of  the  limestones,  or  at  the  junction  of  two  different 
terranes  possessing  different  possibilities  for  the  migration  of 
solutions. 

Such  ore  bodies  are  widely  distributed  and  often  associated 
with  limestones. 

There  are  five,  hydrous  oxides  of  iron  grouped  together  in  this 
discussion  under  the  name  of  limonite,  because  from  a  commercial 
standpoint  all  hydrous  oxides  of  iron  giving  a  brown,  yellowish- 
brown,  or  reddish-brown  streak  are  classified  in  the  trade  as  limo- 
nite. Limonite  is  far  the  most  abundant  mineral  of  the  group 
and  forms  large  ore  bodies.  The  five  hydrous  oxides  are  gothite, 
Fe203,  H20;  xanthosiderite,Fe2O3,2H20;  (limnite,Fe203,3H20); 
turgite,  2Fe203,H20;  limonite,  2Fe2O3,3H20. 

Gothite  is  the  only  mineral  in  the  group  that  is  crystalline. 
The  others  are  amorphous,  and  all  sorts  of  admixtures  between 
them  may  occur.  The  impurities  often  found  in  these  ores 
afford  some  clue  as  to  origin.  They  comprise  sand,  clay,  organic 
matter,  the  carbonates  of  iron,  calcium  and  magnesium,  the  hy- 
droxides of  aluminum  and  manganese,  and  the  phosphate  of 
iron,  vivianite. 

Limonite  may  result  from  the  hydration  of  hematite.  The 
decomposition  of  ferruginous  rocks  in  situ  yield  laterite  which  here 
contains  a  mixture  of  the  iron  and  aluminum  hydroxides.  The 
limonitization  of  pyrite  or  chalcopyrite  is  manifested  in  the  gossan 
caps  often  reaching  to  a  considerable  depth.  Waters  charged  with 

13 


194  ECONOMIC  GEOLOGY 

carbon  dioxide  serve  as  a  solvent  for  the  iron  in  both  the  igneous 
and  the  sedimentary  rocks  and  from  these  solutions  limonite  may 
be- deposited.  According  to  F.  W.  Clarke,  organic  acids  and 
humus  assist  in  the  solution  of  ferrous  compounds  and  furnish  to 
swamp  waters  the  material  from  which  bog  iron  ores  are  formed. 
The  atmospheric  oxidation  of  siderite  affords  the  irridescent 
films  of  ferric  hydroxide  so  often  seen  on  the  surface  of  stagnant 
swamp  waters. 


FIG.  102. — Old  limonite  pit,  Ivanhoe,  Virginia,  showing  pinnacled  sur- 
face of  limestone  which  overlies  the  ore-bearing  clay.  The  level  surface 
before  mining  began  is  seen  on  either  side  of  excavation.  (By  permission 
of  the  Macmillan  Company,  from  Ries1  Economic  Geology.} 

According  to  N.  S.  Shaler,  bog  iron  ores  are  far  more  abundant 
around  the  margin  of  swamps  and  often  wanting  at  the  centers. 
The  deposition  of  the  ore  is  not  always  as  slow  a  process  as  is 
sometimes  supposed.  A.  Geikie  cites  the  accumulation  of  such 
ores  to  a  thickness  of  several  inches  in  26  years  in  some  of  the 
Swedish  lakes.  The  oxidation  of  ferrous  sulphate  solutions  may 
also  yield  limonite.  Acorcding  to  R.  A.  F.  Penrose,  limonite 
may  be  derived  from  glauconite  through  some  process  of  altera- 
tion. It  may  form  a  replacement  deposit  in  limestones,  and  even 
ferriferous  limestones  themselves  may  yield  residuary  limonite. 
(See  Fig.  102.) 


USEFUL  METALS 


195 


Character  of  the  Ore  Bodies. — The  sulphides  of  iron,  pyrite 
and  pyrrhotite,  occur  in  well-defined  fissure  veins,  as  primary 
segregations  from  a  sulphidic  magma,  as  contact  deposits  between 
igneous  and  sedimentary  rocks.  As  stated  earlier,  the  sulphides  of 
iron  play  no  part  in  the  metallurgy  of  the  metal  in  the  United 
States.  Attempts  have  been  made  in  the  southern  Appalachian 
belt  to  manufacture  high-grade  pig  iron  from  sulphides  but  these 
efforts  proved  futile  and  the  process  was  abandoned. 

Magnetite  occurs  (1)  as  lens-shaped  masses  differentiating  from 
a  peridotite  magma  (see  Fig.  103);  (2)  as  lenticular  masses  in  the 
metamorphic  rocks,  this  is  by  far  the  most  important  form  of  the 
ore  bodies  of  magnetite  of  commercial  significance;  (3)  as  contact 


IGNEOUS  VEIN  WITH  SCHLIER£N 


m 


FIG.    103. — Vein   of   norite,   30   to   70   yd.    in   width   with    schlieren  of 
titaniferous  iron  ore.     (After  J.  H.  L.   Vogt.) 

deposits  between  intrusives  and  sedimentaries,  but  often  too 
high  in  titanium  to  be  of  great  commercial  value;  (4)  as  placer 
sands  arising  from  the  decomposition  of  the  higher  rocks,  often 
auriferous,  and  (5)  as  beach  sands  on  the  shores  of  lakes  and  seas. 
Hematite  occurs  as  basin-shaped  replacement  deposits;  as 
bedded  deposits  and  as  contact  deposits.  Limonite  is  often 
residuary.  If  fills  the  cracks,  joint  planes  and  fissures  in  the 
earlier  stages  of  the  decomposition  of  ferriferous  rocks.  It  oc- 
curs also  as  replacement  deposits.  These  are  often  concentrated 
into  beds  of  great  thickness.  In  the  weathering  of  pyritiferous 
ore '  bodies  and  the  leaching  of  chalcopyrite,  limonite  may  be 
formed  in  sufficient  quantities  to  be  of  commercial  significance 


196  ECONOMIC  GEOLOGY 

as  in  the  " Great  Gosson  Lead"  in  Virginia,  and  Ducktown, 
Tennessee. 

Siderite  occurs  in  bedded  deposits  in  the  Carboniferous  ter- 
ranes  of  western  Pennyslvania  and  in  several  other  localities 
along  the  Appalachian  belt.  It  occurs  in  a  clay  bed  lying  beneath 
the  Tertiary  formations  on  the  west  side  of  Chesapeake  bay  for  a 
distance  of  50  miles.  Siderite  often  constitutes  a  large  part  of 
the  clay-iron  stones  of  the  Coal  Measures  and  many  shaly 
stratified  deposits. 

The  impurities  present  in  iron-ore  bodies  fall  into  two  classes: 
(1)  Those  that  are  not  seriously  objectionable  in  small  quantities 
save  as  they  lower  the  iron  content  of  the  ore  and  thereby 
depreciate  the  ore  in  value.  Calcium  carbonate  is  often  present 
in  hematites  that  occur  in  bedded  deposits  between  sandstones 
and  limestones.  If  the  lime  content  is  high  the  carbon  dioxide 
must  be  volatilized  before  smelting  the  ore.  Clayey  matter  is 
often  present  in  limonites  as  admixed  material  that  requires  a 
larger  percentage  of  flux  in  the  treatment  of  the  ore. 

(2)  Impurities  that  tend  to  weaken  the  iron  and  therefore  lessen 
its  value.  Silica  is  undesirable  in  iron  ores  for  two  reasons. 
It  lowers  the  iron  content  of  the  ore  and  requires  a  larger  amount 
of  fluxing  materials  in  its  treatment.  However  foundry  iron 
sometimes  carries  10  per  cent,  or  more  of  silicon.  Sulphur  is 
objectionable  because  of  the  brittleness  imparted  to  the  result- 
ing iron.  It  is  found  as  pyrite  in  the  magnetites  but  it  may  arise 
from  the  presence  of  gypsum  or  barite  in  the  limonites.  Phos- 
phorus is  objectionable  for  the  same  reason.  It  is  present  in 
the  mineral  apatite  associated  with  some  magnetites.  It  should 
not  be  present  in  any  iron  ore  in  excess  of  one-tenth  of  1  per  cent. 
It  cannot  be  volatilized  in  either  the  blast-furnace  or  the  acid 
converter  used  in  the  manufacture  of  Bessemer  steel,  and  there- 
fore it  appears  in  the  finished  product.  Titanium  is  a  common  in- 
jurious constituent  found  in  many  magnetites.  It  does  not  render 
steel  brittle  but  it  renders  the  ore  highly  refractory  and  forces  a 
part  of  the  iron  into  the  slag.  In  the  manufacture  of  titanium 
steel  the  metal  should  be  added  directly  as  an  alloy. 

Geographical  Distribution. — There  are  three  distinct  belts  of 
iron  ores  in  the  United  States.  (See  Fig.  104.) 

(1)  The  Appalachian  district;  (2)  the  Lake  Superior  district; 
and  (3)  the  Cordilleran  section. 

Until  recently  practically  all  of  the  iron  ores  of  the  United 


USEFUL  METALS 


197 


States  came  from  the  eastern  side  of  an  imaginary  line  drawn 
from  Lake  Winnepeg  on  the  north  to  the  eastern  base  of  the 
Rockies,  thence  southward  to  the  Rio  Grande  River.  It  will 
be  remembered  that  practically  all  of  the  gold  in  the  United 
States  comes  from  the  western  side  of  the  same  line. 

(1)  The  Appalachian  district  stretches  in  a  northeasterly 
direction  from  Alabama  on  the  south  to  Newfoundland  on  the 
north,  and  may  itself  be  subdivided  into  three  distinct  fields, 
especially  with  respect  to  age  and  the  character  of  the  ores  in- 
volved. (1)  The  pre-Cambrian  belt  where  the  ores  are  largely 
magnetites  and  specular  hematites.  These  are  especially 


FIG.  104. — Map  showing  distribution  of  hematite  and  magnetite  de- 
posits in  the  United  States.  After  Harder.  (By  permission  of  the  Mac- 
millan  Company,  from  Ries'  Economic  Geology.) 

abundant  in  the  Adirondack  region,  southeastern  New  York, 
northern  New  Jersey,  southeastern  Pennsylvania  and  in  Tennes- 
see. (2)  The  Cambro-Ordovician  ores,  hematite  and  limonite, 
are  distributed  along  the  great  Appalachian  valley,  and  even 
abundantly  in  western  New  England.  (3)  The  Clinton  ore, 
fossiliferous  or  oolitic,  of  Silurian  age.  These  deposits  are  espe- 
cially well  developed  in  central  New  York,  where  they  were  first 
discovered  at  Clinton,  Oneida  County,  N.  Y.,  and  in  Alabama. 
The  terranes  of  the  Adirondack  region  are  almost  exclusively 
pre-Cambrian.  The  exceptions  are  the  occasional  inliers  of 


198  ECONOMIC  GEOLOGY 

Potsdam  sandstone  of  Cambrian  age,  deposited  unconformably 
upon  the  older  formations. 

According  to  J.  M.  Clarke  the  metamorphic  series  consists  of 
the  Grenville  series  of  limestones  and  dolomites,  gneisses  of  both 
acidic  and  basic  character  bearing  the  common  metamorphic 
silicates  together  with  graphite  and  pyrite;  amphibolites  com- 
posed mostly  of  hornblende;  quartzites  and  gneisses.  The  ig- 
neous rocks  consist  of  anorthosites,  gabbros,  syenites,  granites, 
with  later  diabase  dikes. 

The  normal  magnetites  occur  both  upon  the  eastern  and  the 
western  side  of  the  Adirondack  Mountains.  One  of  the  most 
productive  localities  is  Mineville,  which  is  situated  to  the  north- 
west of  Port  Henry.  The  ores  are  granular  masses  of  magnetite, 
lenticular  in  character,  but  often  in  so  nearly  a  horizontal 
position,  and  of  such  length  that  they  appear  like  bedded  ores. 
According  to  Kemp  and  Newland  these  magnetites  are  differ- 
entiation products.  Newland  substantiates  this  theory  by 
noting,  in  the  acid  intrusives  of  the  area  involved,  a  large  excess 
of  iron  above  the  percentages  required  with  the  lime  and 
magnesia  in  the  formation  of  silicates. 

The  titaniferous  magnetites  of  New  York  are  found  chiefly  in 
Essex  and  Franklin  counties.  The  ore  bodies  occur  in  the  intrusive* 
anorthosites  which  are  traversed  by  dikes  of  gabbro.  Small  ore 
bodies  are  found  within  the  gabbro,  in  tabular  form  and  con- 
formable with  the  strike  of  the  dikes.  The  larger  ore  bodies 
in  the  anorthosites  may  represent  differentiation  products 
formed  during  the  solidification  of  the  anorthosite  magma,  or 
they  may  represent  intrusives  forced  into  the  anorthosite  after 
a  partial  solidification  of  the  anorthosite  magma  had  taken  place. 
The  ores  bear  both  titaniferous  magnetite  and  ilmenite,  FeO, 
Ti02-  The  gangue  minerals  associated  with  the  ores  are  the  am- 
phiboles,  the  pyroxenes,  olivine,  and  the  metamorphic  minerals 
spinel  and  garnet. 

The  Cambro-Ordovician  belt  finds  its  best  representative  at 
Cornwall,  Pennsylvania  (see  Fig.  104).  The  ore  bodies  of  mag- 
netite form  large  and  small  masses  of  somewhat  irregular  shape, 
either  within  the  sediments  themselves,  or  at  their  contact  with 
intrusive  Triassic  diabase.  While  the'ores  appear  as  contact  de- 
posits the  characteristic  silicates  of  contact  metamorphic  deposits 
are  largely  wanting  (Fig.  105). 

One  of  the  best  magnetite  beds  in  northern  Vermont  is  found 


USEFUL  METALS  199 

in  Troy  about  two  miles  northeast  of  the  village  bearing  that 
name.  Three  veins  of  the  ore  were  worked  about  the  middle  of 
the  nineteenth  century  and  the  resulting  iron  used  only  locally 
on  account  of  the  great  distance  from  the  railroad.  A  portion 
of  this  ore  was  worked  in  a  foundry  on  the  banks  of  the  Missisquoi 
river  near  the  ore  deposit,  while  a  part  was  shipped  to  St .  Johns- 
bury,  50  miles  distant.  The  freedom  from  sulphur  and  phos- 
phorus of  this  ore  made  it  especially  desirable  for  all  purposes 
where  an  extremely  tough  steel  was  sought.  The  ore  bodies 


FIG.  105. — Magnetite  mine,   Cornwall,    Pennsylvania,  showing  structure 
of  the  ore.     (Photograph  by  T.  C.  Hopkins.) 

represent  primary  segregations  in  a  peridotite  magma  in 
Cambrian  terranes.  They  are  not  worked  at  present. 

In  the  northward  extension  of  this  belt  into  Canada  large 
lenses  of  magnetite  are  encountered  in  Megantic  County, 
Quebec.  These  ore  bodies  are  more  or  less  lens-shaped  and 
occur  near  the  outer  margins  of  the  peridotite  or  even  within 
the  peridotite  itself.  The  ores  represent  differentiation  products 
in  the  peridotite  magma.  The  mines  are  still  prominent  pro- 
ducers. 

The  third  division  of  the  Appalachian  belt  is  widely  known  as 
the  Clinton  ore  of  Silurian  age.  These  ores  are  sometimes 
called  fossil  ore,  pea  ore  and  dyestone  ore,  but  the  term  Clinton 


200  ECONOMIC  GEOLOGY 

ore  is  in  far  more  general  use.  The  ores  are  found  in  many 
localities  from  Alabama  to  Newfoundland,  where  the  Clinton 
terrane  is  represented.  The  ore  bodies  are  interstratified  with 
shales  and  sandstones  and  occur  as  beds  or  lenses  of  varying 
length  and  thickness.  Sometimes  two  beds  will  be  represented 
in  the  same  locality,  and  in  some  cases  three  or  even  four  beds 
may  be  encountered.  In  thickness  the  beds  vary  from  a  few 
inches  to  10  ft.  In  some  instances  where  the  ore  bodies  are  more 
lens-shaped  they  reach  a  thickness  approximating  40  ft. 

In  central  New  York  as  well  as  in  Newfoundland  the  beds  are 
nearly  horizontal,  while  in  the  Appalachian  region  the  dip  at 
times  becomes  quite  high.  Two  varieties  based  upon  texture 
are  well  known.  (1)  The  fossil  ore  which  consists  largely  of 
fossil  fragments.  (2)  The  oolitic  ore  which  consists  of  grains  of 
silica  encircled  by  hematite.  The  ores  at  the  surface  are  low  in 
their  lime  content  from  the  solution  of  the  associated  carbonate, 
and  soft  as  a  result  of  weathering  agencies,  while  the  lower  por- 
tions of  the  ore  body  are  higher  in  lime  and  hard  because  the 
calcium  carbonate  with  which  the  ores  are  associated  has  not 
been  removed. 

At  Birmingham,  Alabama,  the  Clinton  ores  are  of  great  com- 
mercial significance.  The  ore  beds  are  situated  on  Red  Mountain, 
associated  with  sandstones  and  shales,  and  reach  a  maximum 
dip  of  50  degrees  to  the  west.  The  burden  of  the  overlying 
material  is  often  light  and  the  ore  is  mined  by  open-cut  method 
and  by  stopes.  The  peculiar  significance  of  the  field  lies  in  the 
fact  that  to  the  west  of  the  ore  there  is  an  abundance  of  Cambrian 
limestone  for  a  flux,  and  to  the  east  two  coal  basins  for  fuel. 
Thus  all  the  essentials  of  a  successful  pig-iron  industry  exist  at 
Birmingham:  (1)  Iron  ore  for  the  extraction  of  the  metal;  (2) 
limestone  in  close  proximity  for  flux;  and  (3)  coal  in  abundance 
for  fuel. 

According  to  H.  Hies  the  more  important  Clinton  iron-ore 
deposits  may  be  classified  as  follows:  (1)  West  Central  New 
York.  (2)  Several  narrow  belts  in  central  Pennsylvania.  (3) 
Alleghany  County,  Virginia.  (4)Lee  and  Wise  Counties,  Vir- 
ginia, extending  in  a  southwesterly  direction  into  the  La  Follette 
district  in  Tennessee.  (5)  Narrow  belts  in  the  neighborhood  of 
Chattanooga,  Tennessee.  (6)  Birmingham,  Alabama.  (7)  Bath 
County,  Kentucky.  (8)  Dodge  County,  Wisconsin.  (9)  Newly 
discovered  ores  in  Missouri.  (10)  Belle  Isle,  Newfoundland. 


USEFUL  METALS  201 

Three  important  theories  have  been  advanced  to  account  for 
the  origin  of  these  ores. 

(1)  Sedimentary  origin.     James  Hall,  C.  H.  Smyth,  Jr.,  and  S. 
W.  McCallie  have  advocated  that  the  ores  are  of  contemporaneous 
origin  with  the  inclosing  rocks  and  that  they  have  been  deposited 
upon  the  Silurian  sea  floor  as  chemical  precipitates.     Hall  be- 
lieved that  the  essential  iron  of  the  present  ore  was  leached  out 
of  the  older  crystalline  rocks  and  deposited  as  a  chemical  pre- 
cipitate.    Smyth    considers   that  this  leached  iron  was  trans- 
ported from  the  associated  crystalline  areas  into  shallow  basins 
in  the  Silurian  sea  and  deposited  around  sand  grains  or  any  nuclei 
that  were  available.     McCallie  believes  that  the  original  iron 
mineral  was  either  glauconite  or  greenalite.     The  continuation 
of  the  ores  with  depth,  as  in  Alabama  where  the  ores  are  en- 
countered 800  ft.  below  the  surface,  and  in  Missouri  where  the 
ores  have  been  encountered  by  drillings,  is  an  additional  proof  of 
the  sedimentary  origin  of  these  ores. 

(2)  Residual  Enrichment.     I.  C.  Russell  advocated  the  theory 
that  the  Clinton  iron  ores  were  derived  from  ferruginous  lime- 
stones by  weathering  agencies.     The  iron  representing  the  less 
soluble  portions  of  the  formations  would  remain  in  a  more  con- 
centrated form  due  to  the  loss  of  the  limestone  through  solution 
and  transportation.     Russell  cites  a  57  per  cent,  iron  content  at 
the  surface  of  the  Clinton  limestone  near  Attalla,  Alabama,  and 
an  iron  content  of  only  7.75  per  cent,  at  a  depth  of  250  ft.     E.  C. 
Eckel  has  pointed  out  that  at  a  depth  of  250  ft.  the  iron  content 
sometimes  rises  as  high  as  42  per  cent.,  therefore  the  validity  of 
the  theory  is  called  into  question. 

3.  Metasomatic  Replacement  Deposits.  According  to  J.  J. 
Rutledge  the  ores  are  of  much  later  origin  than  the  associated 
terranes.  He  believes  that  the  iron  content  of  the  overlying 
shales  was  leached  out  by  weathering  processes  and  deposited 
as  a  metasomatic  replacement  of  calcium  carbonate  by  the 
anhydrous  iron  oxide.  He  cites  in  substantiation  of  his  theory 
the  following  arguments:  (1)  The  invariable  association  of  the 
soft  rich  ore  with  leached  decolorized  shales  together  with  the 
association  of  the  hard  lean  ores  with  bright  unweathered  shales. 
(2)  The  relation  of  the  ores  with  the  shattered  sandstones  and 
to  the  topographic  situation  of  the  ores.  (3)  The  fact  that  analo- 
gous replacements  are  in  the  process  of  formation  at  the  present 
time  in  the  Medina  sandstone.  (4)  The  progressive  downward 


202  ECONOMIC  GEOLOGY 

transition  of  the  associated  limestones  to  iron  ores  traceable 
both  in  the  field  and  in  the  chemical  laboratory.  (5)  The  absence 
of  crumpling  and  shrinking  of  the  strata,  which  points  to  a  relative 
rather  than  an  absolute  enrichment  of  the  ores  (Fig.  106). 

There  are  many  widely  scattered  occurrences  of  limonite  along 
the  Appalachian  belt.  These  are  especially  abundant  in  Ala- 
bama, Georgia,  Tennessee,  Virginia,  Pennsylvania  and  Vermont. 
The  ores  are  often  of  uncertain  or  variable  composition  on  account 
of  the  admixed  clayey  matter,  silica,  and  in  some  instances 
vegetable  matter.  Beds  of  bog  iron  ore  or  limonite  have  been 
worked  near  Brandon,  Monkton  and  Bennington,  Vermont,  and 
in  several  other  localities  in  the  southern  part  of  the  state. 


m     en     en 

Brow  none  deposits      Hematite  deposits     Magnetite  deposits 


Contact  of  crystalline  rocks      Contact  of  crysta 
and  Paleozoic  sediments  and  coastal  plain  deposits 


FIG.  106. — Map  showing  location  of  iron-ore  deposits  in  Virginia. 
After  Harder.  (By  permission  of  the  Macmillan  Company,  from  Ries' 
Economic  Geology.) 

They  were  at  one  time  of  considerable  commercial  significance. 
The  iron  ores  of  Brandon  were  discovered  in  1810  and  soon  after 
that  some  iron  of  superior  quality  was  manufactured  for  several 
years.  The  limonites  of  Alabama  and  Virginia  furnish  more 
than  50  per  cent,  of  the  hydrated  iron  oxides  in  the  United 
States. 

The  more  important  limonites  are  residual  deposits  forming 
two  distinct  types  of  ore  bodies. 

Residual  Limonites. — These  result  from  the  weathering  of 
vast  areas  of  ferruginous  rocks  and  the  deposits  appear  as  masses 
in  the  residual  clays.  Limonites  may  also  occur  as  bedded  de- 
posits, replacement  deposits,  and  as  bog  ore  deposits  in  swamps 


USEFUL  METALS 


203 


FIG.  107. — View   of  limonite   pit   near   Ironton,    Pennsylvania.     (By  per- 
mission of  the  Macmillan  Company,  from  Ries*  Economic  Geology.} 


.FiG.  108. — Pit   of  residual  limonite,    Shelby,   Alabama.     (By   permission 
of  the  Macmillan  Company,  from  Ries'  Economic  Geology.) 


204  ECONOMIC  GEOLOGY 

and  bogs.  The  residual  limonite  ore  bodies  occur  in  many 
scattered  localities  both  in  the  Blue  Ridge  and  the  Appalachian 
mountains  either  in  the  Cambrian  quartzites  at  or  near  their 
contact  with  the  overlying  limestones  or  in  the  limestones  them- 
selves. The  former  are  called  mountain  ores  and  the  latter  the 
valley  ores  (Fig.  107). 

Gossan  limonites.  These  are  derived  from  the  disintegration 
and  oxidation  of  the  sulphides  of  iron  and  copper  where  the  more 
soluble  constituents  have  been  transferred  downward  for  the 
enrichment  of  the  underlying  ore  bodies  or  carried  elsewhere  in 
solution.  The  ore  in  such  deposits  sometimes  contains  41 
per  cent.  iron.  Corinth  and  Vershire,  Vermont;  Cooper,  Vir- 
ginia; and  Ducktown,  Tennessee,  represent  such  deposits  (Fig. 
108). 

2.  Lake  Superior  District. — This  field  is  by  far  the  most  im- 
portant iron-ore  district  of  the  world.  It  furnishes  more  than 
four-fifths  of  the  iron  ores  of  the  United  States  and  therefore 
more  than  four-fifths  of  the  pig  iron.  The  ores  are  mostly 
hematite,  although  there  is  some  magnetite  in  the  Marquette 
field  in  Michigan  (Fig.  109). 

The  Lake  Superior  region  may  be  further  subdivided  into 
seven  districts  each  worthy  of  a  detailed  description:  (1) 
Mesabi  district  in  Minnesota;  (2)  Vermillion  district  in  Minne- 
sota; (3)  Cuyuna  district  in  Minnesota;  (4)  Marquette  district  in 
Michigan;  (5)  Crystal  Falls  district  in  Michigan;  (6)  Menominee 
district  in  Wisconsin;  and  (7)  Penokee-Gogebic  district  on  the 
Michigan  and  Wisconsin  boundary. 

1.  Mesabi  Range.  The  Mesabi  iron  range  comprises  by  far 
the  most  important  district  in  the  Lake  Superior  region,  and  it 
produces  more  iron  ore  than  all  of  the  others  combined. 

According  to  C.  K.  Leith,  the  geological  section  comprises  at 
its  base  Archean  greenstones,  hornblende  schists  and  porphyries 
which  are  separated  from  the  Lower  Huronian  terranes  by  an 
unconformity.  The  Huronian  terranes  comprise  the  equiva- 
lents of  the  Ogishke  and  Knife  formations  of  the  Vermillion  dis- 
trict, slate-graywacke  formations  and  conglomerates  in  nearly 
vertical  position;  and  granite  intrusives  in  the  lower  formations. 
These  are  separated  from  the  Upper  Huronian  by  another  uncon- 
formity. The  Upper  Huronian  terranes  comprise  the  Biwabik 
iron  formation,  the  Pokegama  quartzite  and  quartz  slate;  and 
the  Virginia  slate.  This  slate  is  separated  in  turn  from  the 


USEFUL  METALS 


205 


Keweenawan  by  another  unconformity.  The  Keweenawan 
formations  consist  of  gabbro  and  granite  intrusives  in  all  of  the 
lower  formations.  All  of  the  foregoing  rocks  are  separated  from 
the  Cretaceous  by  another  unconformity. 


I 

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o 

'C 

-4-3 
03 


I 


The  Biwabik  iron  formation  forms  a  continuous  belt  from 
Grand  Rapids  on  the  west  to  Birch  Lake  on  the  east.  Its  breadth 
varies  from  a  quarter  of  a  mile  to  more  than  two  miles.  It  pre- 
sents four  widely  different  varieties  of  ferriferous  rocks.  (1) 


206  ECONOMIC  GEOLOGY 

A  lean  ferruginous  chert,  the  chert  and  iron  occurring  in  alternate 
bands,  or  irregularly  mixed.  (2)  Iron  ore  bodies.  (3)  Ferrous 
silicate  and  carbonate  rocks.  (4).  Ferruginous  slates. 

The  iron  was  originally  present  in  part  as  a  carbonate  but  mostly 
as  the  silicate,  greenalite.  Surface  waters  charged  with  carbon 
dioxide  attacked  the  greenalite  forming  the  carbonate  of  iron  and 
orthosilicic  acid.  The  iron  carbonate  was  either  taken  into 
solution  and  precipitated  by  contact  with  solutions  bearing  an 
abundance  of  oxygen,  or  else  it  was  oxidized  and  hydrated  in 


FIG.  110. — Iron  mine,  Soudan,  Minnesota,  shows  old  open  pit  with 
jasper  horse  in  middle.  (By  permission  of  the  Macmillan  Conpany,  from 
Ries'  Economic  Geology.) 

situ.  The  removal  of  the  orthosilicic  acid  in  solution  is  cited  as 
responsible  for  the  slumping  of  the  beds  at  the  contact  of  the  wall 
rock  and  the  ore  bodies. 

2.  The  Vermillion  District:  According  to  J.  M.  Clements 
this  district  comprises  a  narrow  belt  of  Archean  rocks  in  places 
overlain  by  those  of  the  Huronian  series  extending  in  a  north- 
easterly direction  from  Vermillion  Lake,  Minnesota,  to  Gunflint 
Lake  on  the  International  Boundary,  a  distance  of  about  92 
miles.  The  district  is  one  of  extremely  complex  folding.  Super- 
imposed upon  the  longitudinal  folds  are  cross  folds  with  steep 


USEFUL  METALS  207 

pitches  which  shows  that  the  transverse  folding  was  intense. 
The  structure  of  the  district  is  further  complicated  by  intrusives 
of  various  ages.  Unlike  the  other  districts  the  iron  ores  occur  in 
the  Achean,  Lower  Huronian  and  Upper  Huronian  formations. 
It  differs  also  in  that  the  chief  producer  of  iron  ores  is  the  Archean 
formation.  The  ores  occur  in  the  upper  portion  of  the  Archean 
terranes  known  as  the  Soudan  iron  formation.  It  consists  of 
cherty  iron  carbonates,  ferruginous  cherts,  pyritic  quartz  rocks, 
jaspilites  and  ore  bodies.  The  ore  bodies  are  usually  near  the 
base  of  the  formation  and  occur  in  synclinal  troughs  in  the  green- 
stones. At  Soudan  the  ore  bodies  are  underlain  in  part  by  the 
greenstones  and  in  part  by  the  associated  porphyries  (Fig.  110). 

The  Lower  Huronian  iron-bearing  terrane  is  known  as  the 
Agawa  formation.  The  ores  occur  chiefly  in  the  eastern  part  of 
the  district  on  Hunter's  Island,  Canada.  The  formation  con- 
sists of  ferruginous  cherts,  ferruginous  slates,  jaspilites  and  iron- 
bearing  carbonates. 

The  Upper  Huronian  iron-bearing  terrane  is  known  as  the  Gun- 
flint  formation.  It  is  confined  to  the  northeast  part  of  the  district 
west  of  Gunflint  Lake.  It  consists  of  carbonaceous  slates,  fer- 
ruginous slates,  and  jaspilites,  in  the  vicinity  of  Gunflint  Lake, 
but  to  the  southwest  it  passes  into  amphibolitic  and  magnetic 
quartz  rock  due  to  the  metamorphism  of  the  associated  gabbros. 

3.  The   Cuyuna   District:     This   range  is   southwest   of  the 
Mesabi  range  in  Minnesota.     The  formations  include  quartzites 
and  their  altered  equivalents,  iron  formations,  slates,  together  with 
intrusive  granites  and  diorites.     The  ore  occurs  in  lenses  from 
100  to  250  ft.  in  thickness. 

4.  The  Marquette  District:     This  district,  according  to  C.  R. 
Van  Hise,  W.  S.  Bayley  and  H.  L.  Smyth,  comprises  a  compara- 
tively small  east  and  west  belt  situated  wholly  within  the  state 
of    Michigan.     The    geological    section    comprises    formations 
ranging  from  the  Archean  to  the  Cambrian.     The  iron-bearing 
formations  occur  in  all  four  of  the  horizons  at  which  iron  ores 
are  found  in  the  Lake  Superior  region;  viz.,  The  Archean,  the 
Negaunee  formation  of  the  Middle  Huronian,  and  in  two  horizons 
in  the  Upper  Huronian,  the  one  at  the  base  of  the  Goodrich 
quartzite  and  the  other  in  the  Bijiki-formation.     Negaunee  is  the 
chief  iron-producing  district.     It  consists  of  cherty  iron  carbonates, 
ferruginous  slates,  ferruginous  cherts,  jaspilites,  griinerite  magne- 
tite schists,  detrital  fragmental  rocks  and  iron-ore  bodies  (Fig.  111). 


208 


ECONOMIC  GEOLOGY 


According  to  Van  Hise  the  orginal  iron  ore  formation  was  a 
cherty  iron-bearing  carbonate  which  in  some  localities  closely 
approached  a  siderite.  The  upper  part  of  the  Negaunee  formation 
in  Inter-Marquette  times  was  transformed  into  ferruginous  slates 
and  ferruginous  cherts.  In  the  early  Upper-Marquette  time  de- 
trital  material  from  the  Negaunee  formations  accumulated.  This 
material,  formed  at  the  base  of  the  Upper-Marquette  series,  con- 
sisted of  iron  oxide  and  quartz.  Thereafter  the  original  rock 
masses,  the  weathered  rocks  in  situ,  and  the  detrital  material 
were  all  buried  beneath  Upper-Marquette  sediments  and  igneous 
rocks  of  Upper-Marquette  and  Keweenawan  age. 

While  these  rocks  were  deeply  buried  they  were  intensely 
folded.  Where  the  original  carbonate  of  iron  remained  and  es- 
pecially where  it  was  intruded  by  abundant  igneous  rocks  it  was 
partly  transformed  into  a  grtinerite  magnetite  schist.  The  iron 


FIG.  111. — Generalized  section  in  the  Marquette  district  showing  the 
relation  of  all  classes  of  ore  deposits  to  the  associated  formations.  (After 
C.  R.  Von  Hise,  U.  S.  Geological  Survey.) 

oxide  of  the  ferruginous  slate  and  ferruginous  cherts  was  dehy- 
drated and  these  rocks  were  transformed  to  jaspilites.  The  de- 
trital ores  were  converted  into  hematite  and  jasper  quartzites  and 
conglomerates.  Subsequent  to  this  period  of  folding,  but  prior 
to  Cambrian  time,  the  region  was  folded  anew.  Denudation 
cut  through  the  Upper-Marquette  formation  and  again  exposed 
the  Negaunee  terranes  to  the  processes  of  weathering.  Where 
the  unaltered  cherty  iron  carbonate  was  abundant  it  was  trans- 
formed into  ferruginous  slates  and  cherts.  It  was  at  this  period  of 
alteration  that  the  ore  deposits  were  developed. 

According  to  E.  T.  Hancock  the  workable  deposits  of  the 
Negaunee  formation  may  be  divided  into  three  classes.  (1) 
Ore  deposits  at  the  base  of  the  iron-bearing  formation.  (2) 
Ore  deposits  within  the  iron-bearing  formation.  (3)  Ore  de- 
posits at  the  top  of  the  Negaunee  formation  and  at  the  base  of 
the  Goodrich  quartzite. 


USEFUL  METALS  209 

5.  The   Crystal   Falls   District:     This   district,  according  to 
J.  M.  Clements,  H.  L.  Smyth,  W.  S.  Bayley,  and  C.  R.  Van  Hise, 
comprises  a  geological  section  extending  from  the  Archean  to  the 
Cambrian.     The  ore  bodies  occur:  (1)  In  the  Mansfield  slate 
where  only  one  ore  body  of  considerable  dimensions  has  been 
worked.     This  varies  from  16  to  32  ft.  in  thickness  and  stands  in 
almost  vertical  position,  (2)  also  in  the  Negaunee  or  Groveland 
iron  formations  where  the  ore  bodies  are  comparatively  small 
and  the  ore  mainly  a  hard  and  siliceous  hematite,  and  (3)  within 
the  Michigamme  formation  where  the  large  deposits  at  Crystal 
Falls  occur.     The  ore  is  chiefly  a  soft  red  hematite,  though  fre- 
quently hydrated  and  classified  in  the  trade  as  brown  hematite. 

No.  1  is  in  the  Lower  Middle  Huronian  formations.  No.  2 
is  in  the  Upper  Middle  Huronian  formations.  No.  3  is  in  the 
Upper  Huronian  formations. 

6.  The  Menominee  District.     This  district,  according  to  C.  R. 
Van  Hise  and  W.  S.  Bayley,  lies  mostly  in  Wisconsin  and  the 
geological  section  extends  from  the  Archean  to  the  Ordovician. 
The  ore  bodies  occur:  (1)  In  the  Traders  ore-bearing  member 
which   is   Middle   Huronian.     (2)  In   the  Brier  slate  which  is 
conformable  with  the  Traders  iron-ore-bearing  member  also  of 
Middle  Huronian  age.     (3)  In  the  Curry  ore-bearing  member 
which  lies  conformably  upon  the  Brier  slate  formation  and  of  Mid- 
dle Huronian  age.     Rare  bodies  of  ferruginous  slate  and  iron 
oxide  occur  in   the  Upper  Huronian  formations.     The  ores  of 
the  Menominee  district  are  mainly  gray,  finely  banded  hematite 
with  lesser  amounts  of  a  flinty  hematite  which  shows  local  banding. 

7.  The  Penokee-Gogebic  District.     According  to  R.  D.  Irving 
and  C.  R.  Van  Hise,  this  district  comprises  a  narrow  belt  south 
of  Lake  Superior  with  strike  north  70  degrees  east.     The  most 
productive  portion  of  the  belt  lies  in  Michigan  and  the  remain- 
der in  Wisconsin.     The  geological  formations  are  the  Archean, 
Lower  Huronian,  Upper  Huronian,  Keweenawan  and  Cambrian. 
Each  is  separated  from  its  successor  by  an  unconformity.     The 
ore  bodies  occur  in  the  Upper  Huronian  terranes,  which  consist  of 
a  quartzitic  slate  and  the  Ironwood  formation,  above  which  is  the 
Tyler  slate.     The  ore  bodies  closely  resemble  those  in  the  Mesabi 
district  in  that  they  occur  between  two  slate  belts. 

Previous  to  the  introduction  of  great  masses  of  igneous  rocks 
in  Keweenawan  times  the  original  cherty  iron  carbonate  was 
largely  decomposed  with  the  production  of  some  magnetite,  and 

14 


210 


ECONOMIC  GEOLOGY 


some  actinolite,  forming  an  actinolitic  magnetite  schist  which 
meteoric  waters  were  unable  to  transform  into  a  productive  ore 
body.  The  productive  portion  remained  through  this  period  as 
a  slightly  altered  cherty  iron  carbonate.  When  in  subsequent 
times  the  district  was  folded  and  erosion  was  carried  to  the  extent 
that  the  iron-bearing  formations  were  exposed  to  the  action  of 
meteoric  waters,  the  siderite  was  altered  to  ferruginous  slate, 
ferruginous  chert  and  iron  ores.  A  soft  hydrated  ferric  oxide 
constitutes  the  main  part  of  the  ore.  Hard  slaty  ore  is  not  un- 


LACCOLITHIC 
ANDESITE 


FIG.  112. — Map  of  a  portion  of  the  Iron  Springs,  Utah,  district,  showing 
occurrence  of  iron  ore  in  limestone  near  andesite  contact  and  also  in  the 
igneous  rock.  After  Leith  and  Harder.  (By  permission  of  the  Macmillan 
Company,  from  Hies'  Economic  Geology.} 

common,  and  the  oxides  of  manganese  occur  in  a  few  deposits. 

3.  The  Cordilleran  Section. — There  are  many  widely  scattered 
occurrences  of  iron  ores  in  the  Cordilleran  section.  Many  of 
these  are  not  worked  owing  to  the  long  distance  from  the  rail- 
road, or  a  limited  demand  for  iron,  or  the  character  of  the  ores 
(Fig.  112). 

In  the  southern  part  of  Gunnison  county,  Colorado,  there  is 
a  quantity  of  magnetite  in  the  Cebolla  district.  According  to  J. 
T.  Singewald,  Jr.,  the  ores  occur  (1)  in  the  basic  igneous  rocks. 


USEFUL  METALS  211 

(2)  in  the  basic  igneous-limestone  complex;  (3)  in  the  limestones 
themselves. 

1.  Ores  in  the  Basic  Igneous  Rocks:     The  richer  ores  consist 
of  aggregates  of  titaniferous  magnetite  and  bunches  of  dark 
brown  mica.     In  such  ores  the  pyroxenes  are  not  abundant,  but 
the  ores  pass  into  leaner  varieties  in  which  the  pyroxenes  are  abun- 
dant and  finally  into  a  rock  consisting  almost  exclusively  of  pyrox- 
ene.    There  is  little  evidence  of  the  occurrence  of  large  ore  bodies 
but  rather  of  the  occurrence  of  a  large  number  of  small  ore  segre- 
gations.    The  composition  of  the  ores,  their  mineralogical  asso- 
ciation, and  their  manner  of  occurrence  establishes  beyond  doubt 
their  genetic  position.     They  are  magmatic  segregations  of  titanif- 
erous magnetites  in  a  basic  igneous  rock. 

2.  Ores  in  the  Basic  Igneous-limestone  Complex:     The  most 
interesting  feature  of  this  complex  is  the  occurrence  of  small  de- 
posits of  contact  metamorphic  ore.     The  metamorphic  rock  is 
made  up  of  calcite,  augite,  garnet,  and  less  abundantly,  zoisite 
and  vesuvianite.     Within  the  contact  metamorphic  rock  are 
numerous  pockets  and  nests  of  magnet  te.     The  ores  consist  of 
ilmenite  and  magnetite.     The  most  important  and  striking  fea- 
ture of  the  district  is  the  occurrence  of  highly  titaniferous  mag- 
netite of  contact  metamorphic  origin. 

3.  Ores  in  the  Limestone:   The   limestone  in  this  district, 
wherever  exposed,  has  been  more  or  less  replaced  by  iron.     On 
Iron  Hill  the  ore  is  principally  siderite  and  limonite.     In  the 
small  hill  to  the  north  the  resulting  product  is  chiefly  a  yellow 
ferruginous  j  asper  and  a  highly  siliceous  limonite.     In  some  places 
the  siderite  has  been  changed  to  hematite,  but  the  structure  and 
cleavage  of  the  siderite  are  still  preserved. 

An  analysis  of  the  ore  cited  in  the  same  paper  gives  the  iron 
protoxide  as  8.46  per  cent,  and  the  iron  peroxide  as  69.04  per  cent. 

Hematite  deposits  also  occur  in  Carbon  and  Laramie  Counties, 
Wyoming,  in  the  pre-Cambrian  schists.  Those  in  the  Hartville 
district  in  the  latter  county  are  of  the  greatest  commercial  sig- 
nificance. The  more  important  ore  bodies  occur  as  lenses  in  the 
schists  with  a  foot  wall  of  limestone.  In  some  instances  it  fills 
the  joint  planes  and  breccia  cavities.  Two  grades  of  ore  are 
found  in  this  district.  One  a  hard  hematite  with  about  60  per 
cent,  iron  content.  The  other  is  a  soft,  greasy,  hydrated,  reddish- 
brown  ore.  This  ore  has  been  derived  from  the  hard  variety  by 
the  action  of  waters. 


212  ECONOMIC  GEOLOGY 

According  to  Ball  the  ore  was  deposited  by  descending  waters. 
It  occurs  along  zones  of  maximum  downward  circulation.  Lenses 
and  veins  are  found  along  joints  in  the  rock  masses  at  a  consider- 
able distance  from  the  main  body.  The  associated  minerals  are 
quartz,  calcite  and  limonite  which  have  been  deposited  from  solu- 
tion. In  this  case  the  magnetite  and  the  pyrite  of  the  overlying 
schists  would  be  the  source  from  which  the  circulating  solutions 
derived  the  iron. 

In  Iron  Mountain,  Wyoming,  titanif erous  magnetites  are  found 
in  dikes  traversing  anorthosites.  The  mountain  itself  is  more 
than  a  mile  in  length  and  the  iron-bearing  ridge  is  about  600  ft. 
in  width.  The  ore  which  is  in  the  form  of  a  dike  extends  the 
length  of  the  ridge  and  varies  from  40  to  300  ft.  in  width.  It  is 
flanked  upon  either  side  by  the  anorthosite  and  paralleled  by 
numerous  smaller  dikes.  The  presence  of  similar,  minerals  in 
both  the  anorthosite  and  the  dikes,  although  the  proportions  vary 
somewhat,  suggests  that  they  are  differentiation  products  of  the 
same  magma  with  the  iron  intruded  after  the  complete  solidifica- 
tion of  the  anorthosite.  The  impurities  in  the  dike  material 
are  olivine,  biotite  and  feldspar.  The  percentage  of  iron  is 
about  50.  Lenticular  masses  of  granite  are  also  found  asso- 
ciated with  the  anorthosite.  The  granite  is  also  traversed  by  a 
pegmatite  bearing  magnetite  and  biotite.  In  order  of  age  the 
intrusives  of  the  district  may  be  given  as  anorthosite,  iron  ores, 
granite,  pegmatite. 

Hanover,  New  Mexico:  A  comparatively  new  field  for  the 
production  of  iron  ore  is  near  Hanover,  New  Mexico.  The 
geological  relations  are  fairly  simple.  A  quartz  diorite  porphyry 
has  intruded  Carboniferous  limestones  and  other  sediment aries. 
In  a  part  of  the  area  the  intrusion  has  caused  extensive  met- 
amorphism  of  the  terranes,  and,  along  the  contact  zone,  ores  of 
iron,  copper,  and  zinc  have  been  deposited.  The  ore  is  primarily 
magnetite  but  in  part  it  is  hematite.  The  ores  are  both  hard  and 
soft.  Of  the  former  there  are  three  large  lenticular  masses  and 
numerous  outcrops  that  appear  to  have  the  same  mode  of  occur- 
rence. The  soft  ores  occur  at  several  places  along  the  contact 
between  the  igneous  and  sedimentary  rocks.  The  ore  content 
is  estimated  by  Paige  as  between  53  and  57  per  cent.  Solutions 
from  the  heated  magma,  probably  above  the  critical  temperature, 
impregnated  certain  strata  of  the  surrounding  rocks.  Adjust- 
ments due  to  cooling  served  to  make  the  contact  zone  favorable 


USEFUL  METALS 


213 


for  superheated  gases.  Magnetite,  which  several  investigators 
have  shown  might  be  precipitated  from  iron  silicates  by  reaction 
with  lime,  replaced  the  limestone,  and,  in  part,  the  porphyry  mass. 


I.  l»EAL  SECTION  ACROSS  THE  RECKON  DuWNC  ARCMCAN  TIMES. 


THE  SAME  AS  II,  SHOWINQ  WE,  QROWTM  OF  THE  BOOLPER  ORE  BEDS. 


THE  8AMC  AS  III.  AFTER   BCINq  COVERED  BY  T«E  CAMBRIAN  JEPOJITS 


SECTION  ACROJ*  THC3AMC  ReftlOM.  »MOWrN4  THS  PRISCNT  fTATK. 


FIG.  113. — A  group  of  ideal  sections  showing  the  probable  history  of  the  iron 
ores  of  Pilot  Knob,  Missouri.     (After  Nason.) 

There  are  other  occurrences  of  iron  ores  in  the  United  States 
that  are  of  commercial  importance,  as  shown  in  Figs.  113  and 
114. 


SECTION  THROUGH  THE  PROSblR  IRON  MINE  ,  NEAR  OSWIG.O  .ORCQON. 
(MODiriED    TROM    PUTMAN.) 

FIG.  114. — Section    through    the    Prosser    mine,    near    Oswego,    Oregon. 
(Modified  from  Putnam.} 

Numerous  masses  of  igneous  rocks  belonging  to  the  gabbro 
and  norite  families  are  found  in  the  southern  part  of  Norway  and 
Sweden  (see  Fig.  115).  In  these  masses  are  found  some  of  the 


214  ECONOMIC  GEOLOGY 

most  famous  iron-ore  deposits  of  the  world.  The  iron  ores  occur 
partly  as  segregations  in  the  norite  dikes  and  partly  as  veins,  or 
basic  zones  in  the  anorthosites. 

According  to  Thomas  and  MacAllister  the  iron  ores  in  the 
norite  dikes  at  Storgangen  consist  of  an  intimate  mixture  of 
ilmenite  and  hypersthene,  together  with  a  little  labradorite. 
The  iron- ore  deposits  of  Taberg,  Sweden,  are  titaniferous  and  are 
rich  in  olivine  rather  than  hypersthene.  The  Taberg  ores  and 
their  associated  gabbros  are  regarded  as  having  their  origin  in 
the  same  igneous  reservoir. 

In  the  Ural  Mountains  there  are  several  well  known  districts  in 
which  iron-ore  deposits  are  associated  with  porphyritic  rocks. 
The  porphyries  consist  largely  of  orthoclase,  plagioclase,  augite, 
sometimes  with  the  original  augite  metamorphosed  into  horn- 
blende. The  segregations  from  these  masses  are  largely  mag- 


3  2  3 

FIG.  115. — Section  to  illustrate  the  mode  of  occurrence  of  iron  ores 
in  the  Ekersund — Soggendal  district.  (After  Thomas  and  MacAlister's 
Geology  of  Ore  Deposits.) 

netites  which  occur  as  irregular  patches  and  veins  passing  by 
insensible  gradations  into  the  country  rock. 

The  iron  ores  of  Lorraine  and  Luxemburg,  Europe,  have  a 
variable  composition.  The  ores  exist  as  oxides,  including  mag- 
netites, also  as  carbonate  and  silicate.  The  ores  are  due  in  a 
large  measure  to  contemporaneous  replacements  and  in  part  to 
original  depositions. 

The  hematite  deposits  of  southern  Wales,  Cumberland  and 
Lancashire  occur  in  the  Carboniferous  limestones  and  may  be 
due  to  the  leaching  of  iron  compounds  from  the  overlying  Per- 
mian terranes  and  the  subsequent  deposition  of  the  iron  ores  by 
metasomatic  action. 

The  iron  ores  from  the  Island  of  Elba,  often  beautifully  crystal- 
lized, have  found  their  way  into  nearly  all  museums.  Upon  the 
island  there  are  four  distinct  districts:  Rialtano,  Rio,  Terra-Nova 
and  Calamita.  Limonites  and  magnetites  are  present  as  well  as 


USEFUL  METALS  215 

hematites.  They  occur  as  replacement  deposits  in  limestones  of 
Triassic  age.  Sometimes  all  traces  of  the  original  limestones 
have  been  removed  and  so  complete  has  been  the  interchange  of 
material  that  a  fairly  compact  bed  of  ore  rests  directly  upon  the 
associated  underlying  Paleozoic  rocks.  It  appears  to  be  generally 
accepted  that  the  replacement  of  the  limestone  was  brought  about 
by  ferruginous  solutions  which  found  their  way  into  the  calca- 
eous  rocks  in  post-Eocene  times. 

Geological  Horizon. — Iron  ores  are  comfined  to  no  particular 
geological  age.  They  are  especially  abundant  in  the  pre-Cam- 
brian,  Cambrian,  Ordovician,  Silurian,  Carboniferous  and  Terti- 
ary ages.  Bog  iron  ores  are  in  the  process  of  formation  even  at 
the  present  time. 

Methods  of  Extraction. — At  the  Illinois  Steel  Works  of  South 
Chicago  the  ore  used  in  the  manufacture  of  pig  iron  comes  from 
the  Lake  Superior  district.  The  ore  is  removed  from  boats  by 
means  of  electric  cranes  and  transported  either  to  the  storage 
yards  or  to  the  furnaces  for  immediate  treatment.  The  type  of 
furnace  used  is  known  as  the  blast  furnace.  Each  furnace 
shaped  like  an  inverted  bottle  is  about  80  ft.  high  and  tapers 
more  rapidly  toward  the  base  than  toward  the  top.  The  upper 
part  of  the  furnace  into  which  the  ore,  coke  and  limestone  are 
fed  is  called  the  throat.  From  the  throat  down  to  the  widest 
part  of  the  furnace  it  is  called  the  stack.  The  lowest  part  is 
called  the  bosh.  The  part  of  the  furnace  on  which  the  ore  lies 
is  called  the  hearth.  Here  is  where  the  greatest  heat  is  produced 
and  where  the  ore  is  smelted.  About  4  ft.  above  the  hearth  are 
the  tuyeres  through  which  a  blast  of  air  is  introduced  into  the 
furnace.  The  blast  is  heated  by  the  hot  gases  which  are  generated 
in  the  furnace.  The  zone  of  fusion  is  just  above  the  place  where 
the  bosh  joins  the  hearth.  The  fluid  iron  sinks  to  the  bottom 
of  the  furnace  while  the  resulting  slag  with  its  lighter  specific 
gravity  floats  on  the  surface  of  the  molten  metal.  The  slag  is 
drawn  off  into  V-shaped  troughs  through  which  a  stream  of  cold 
water  is  flowing.  The  slag  is  therefore  shorted  and  transported 
to  large  cylindrical  tanks  from  which  it  is  subsequently  removed 
and  utilized  in  the  manufacture  of  cement. 

The  molten  metal  is  drawn  off  into  ladles  containing  about 
20  tons  each  or  into  sand  troughs  each  containing  about  300  Ib. 
of  the  metal.  These  bars,  not  unlike  cord  wood  in  shape,  are 
pig  iron. 


216  ECONOMIC  GEOLOGY 

Bessemer  steel  is  made  by  burning  out  the  impurities  of  the 
iron  by  blowing  air  through  the  molten  metal,  then  restoring 
enough  carbon  to  form  steel.  The  impurities  of  the  pig  iron  are 
carbon  resulting  from  the  coke  used  as  a  fuel,  silicon,  sulphur 
and  phosphorus  in  the  original  ore.  The  pig  iron  is  placed  in  a 
pear-shaped  converter  lined  with  a  basic  brick,  usually  mag- 
nesite,  chromite  or  bauxite.  At  the  bottom  of  the  converter  the 
air  is  introduced  from  a  compressor  at  a  pressure  of  about  25  Ib. 
per  square  inch.  The  air  forces  its  way  up  through  the  molten 
metal  and  oxidizes  the  impurities.  Phosphorus,  however,  is  not 
removed  by  this  process.  Ferromanganese  or  spiegeleisen,  alloys 
.  containing  a  definite  percentage  of  manganese,  are  then  intro- 
duced in  a  molten  condition.  Instantly  all  the  oxygen  in  the 
molten  iron  unites  with  the  manganese  while  the  carbon  is  taken 
up  by  the  iron,  and  Bessemer  steel  is  the  resulting  product. 
The  steel  is  tough,  elastic  and  widely  utilized. 

Space  might  be  given  co  the  details  of  the  manufacture  of 
foundry  and  forge  iron,  basic  pig  iron,  charcoal  iron,  wrought 
iron,  spiegeleisen  and  f erromanganese ;  also  open-hearth  steel, 
electro-metallurgy  of  iron  and  steel  and  a  combination  of  the 
electro-open-hearth  and  electro-Bessemer  processes.  These  fields, 
however,  lie  in  the  domain  of  metallurgy  rather  than  in  economic 
geology. 

Uses  of  the  Metal. — The  uses  of  iron  are  too  well  known  to  be 
enumerated  in  detail.  The  larger  uses  fall  into  three  distinct 
fields.  1.  Railroad  construction.  2.  Bridge  architectural  con- 
struction. 3.  The  construction  of  vessels. 

While  there  are  many  crucible  steel  plants  scattered  through- 
out the  United  States,  Pittsburg  and  Syracuse  are  the  only 
cities  possessing  more  than  one  such  plant.  The  chief  product  of 
the  two  crucible  steel  plants  in  Syracuse  is  high-grade  tool  steel 
and  used  largely  for  twist  drills,  taps,  dies,  punches,  and  high- 
speed steel  which  is  standard  not  only  throughout  the  United 
States  but  the  world  as  well. 

Another  type  of  steel  manufactured  in  Syracuse  is  magnet 
steel  which  up  to  the  beginning  of  the  present  century  was  largely 
imported.  This  permanent  magnet  steel  is  largely  used  in  elec- 
trical measuring  instruments,  telephones  and  magnetos. 

The  needle  steel  of  Syracuse  is  widely  used  in  domestic  circles 
but  it  is  also  sent  to  England  and  Germany.  The  razor  steel  is 
sold  in  Solingen  which  is  the  cutlery  center  of  Germany.  The 


USEFUL  METALS  217 

crucible  steel  plants  also  manufacture  annular  ball  bearings 
largely  demanded  by  automobiles. 

Electric-furnace  steel  is  also  manufactured  in  Syracuse  and 
largely  used  in  springs,  gears,  shafts,  stearing  knuckles,  and  all 
important  parts  of  automobile  construction.  It  is  estimated 
that  $3,000,000  is  invested  in  the  steel  industry  of  the  city  and 
that  it  stands  second  in  the  country  in  the  quantity  of  its  output 
and  first  in  quality  of  the  steel  manufactured. 

An  ore  to  be  of  value  at  the  present  state  of  the  iron  industry 
must  occur  in  close  proximity  to  a  good  market,  must  be  of  good 
quality  and  large  quantity,  and  must  be  favorably  situated  for 
extraction  and  smelting.  The  most  favorable  location  for  such 
a  mine  is:  (1)  Near  good  coking  coal  for  fuel.  (2)  Near  limestone 
for  a  flux  which  should  not  contain  more  than  5  per  cent,  of  mag- 
nesium carbonate.  (3)  Where  economical  methods  of  trans- 
portation exist.  Unless  these  three  requisites  a  e  observed  iron 
ores  cannot  be  extensively  mined  with  profit  save  where  the  ore 
is  in  great  abundance  and  the  most  economical  methods  of  trans- 
portation exist.  Iron  is  now  so  cheap  that  where  mine  operations 
are  difficult,  as  in  deep  mines,  narrow  veins,  abundant  gangue 
minerals,  and  difficult  transportation,  it  cannot  be  mined  with 
profit.  There  are  enough  good  mines  to  make  selection  possible, 
but  the  iron  of  the  smaller  mine  may  be  obtained  by  electrolysis 
which  now  bids  fair  to  revolutionize  the  iron  industry  of  the 
world. 

The  value  of  iron  in  the  arts  and  industries  depends  upon  the 
fact  that  it  is  abundant  and  cheap;  that  by  different  processes 
it  can  be  made  either  brittle  or  malleable ;  soft,  hard,  or  extremely 
tough.  The  hardness  is  varied  by  heating  and  tempering.  Sev- 
eral metals  such  as  chromium,  nickel,  molybdenum,  titanium, 
vanadium,  tungsten  and  manganese  render  steel  extremely  hard 
and  tough. 

Pig  iron  is  converted  into  steel  on  account  of  the  superiority 
of  steel  for  structural  purposes,  and  the  ever-cheapening  proc- 
esses of  its  manufacture.  Large  engines,  locomotives,  cars,  etc., 
are  now  made  of  steel  rather  than  cast  iron  because  of  its  superior 
strength  and  resistance. 

Three  countries,  the  United  States,  United  Kingdon,  and 
Germany  produce  more  than  three-fourths  of  the  pig  iron  of  the 
world  and  likewise  approximately  four-fifths  of  the  world's  pro- 
duction of  steel.  The  United  States  alone  produces  more  than 


218  ECONOMIC  GEOLOGY 

one-third  of  the  world's  yield  of  each  of  these  commodities.  The 
value  of  pig  iron  produced  in  the  United  States  for  the  banner 
year  of  1907  was  $529,958,000. 

Aluminum :  Its  Properties,  Occurrence  and  Uses 

Properties. — Aluminum,  symbol  Al,  is  a  tin-white,  lustrous 
metal.  It  is  ductile,  sectile  and  malleable.  It  is  a  good  conduc- 
tor of  both  heat  and  electricity.  It  is  permanent  in  either  dry 
or  moist  atmosphere.  Aluminum  is  scarcely  attacked  by  nitric 
acid,  but  is  readily  soluble  in  hydrochloric  acid.  It  is  extremely 
sonorous,  for  when  struck  it  emits  a  clear  and  sustained  note. 
It  has  a  tensile  strength  of  about  35,000  Ib.  per  square  inch. 
It  is  the  lightest  of  all  the  useful  metals.  Its  specific  gravity  is 
2.58,  melting  point,  657.3°  C.,  and  its  atomic  weight  is  27.1. 

Ores  of  Aluminum. — Aluminum  is  the  most  widely  distributed 
of  all  the  metals,  but  it  does  not  occur  free  and  uncombined  in 
nature  on  account  of  its  remarkable  affinity  for  oxygen.  All  of 
the  aluminum  minerals  save  the  double  fluoride,  cryolite,  are 
oxygenated  compounds.  It  does  not  occur  in  nature  alloyed  with 
other  metals.  It  is  unlike  all  the  other  metals  considered  in  this 
volume  save  gold  in  that  its  sulphide  does  not  exist  in  nature. 
The  most  important  source  of  many  of  the  useful  metals  is  the 
sulphide,  but  aluminum  finds  its  most  important  ores  like  iron 
in  the  oxides  and  hydrous  oxides. 

Corundum,  A12  O3,  52.9  per  cent.  Al.  Distinguished  from  all 
other  minerals,  save  the  diamond,  by  its  superior  hardness. 

Ruby,  A1203,  59.2  per  cent.  Al.  The  red  variety  of  corundum 
used  as  a  gem. 

Sapphire,  AUOs,  59.2  per  cent.  Al.  The  blue  variety  of  corun- 
dum used  as  a  gem. 

Emery,  xA^Os,  yFe2O3.  The  oxide  of  aluminum  sometimes 
contains  as  high  as  35  per  cent.  Fe.  Magnetite  may  replace  the 
hematite. 

Diaspore,  A12O3,  H20,  85  per  cent.  A12O3. 

Bauxite,  A1203,  2H20,  73.9  per  cent.  A12O3. 

Gibbsite,  A1203,  3H2O,  65.4  per  cent.  A12O3. 

Cryolite,  A1F3,  3NaF,  12.8  per  cent.  Al. 

Turquoise,  A1203,  P2O5,  5H20.     The  mineral  is  used  as  a  gem. 

Alunite,  K2O,  3A1203,  4S03,  6H2O. 

Alunogen,  A12(S04)3,  18H2O. 


USEFUL  METALS  219 

The  aluminum  minerals  may  be  divided  into  five  distinct 
classes  sollows:  (1)  Those  used  for  the  extraction  of  the  metal; 
corundum,  cryolite,  bauxite  and  gibbsite.  (2)  Those  used  directly 
as  gems;  ruby,  sapphire  and  turquoise.  (3)  Those  used  as  an 
abrasive  on  account  of  their  superior  hardness;  corundum,  emery 
and  diaspore.  (4)  Those  known  directly  as  alums  or  used  in  the 
manufacture  of  alums ;  alunogen  and  alunite,  together  with  many 
natural  alums.  (5)  The  anhydrous  and  hydrous  silicates  bearing 
aluminum. 

Aluminum  occurs  as  an  essential  constituent  of  all  important 
rocks,  save  the  limestone,  marbles,  dolomites  and  sandstones, 
and  even  here  it  is  a  common  impurity.  It  is  present  in  all  the 
micas  and  feldspars  that  have  wide  industrial  application.  It  is 
a  necessary  constituent  of  all  clays. 

Origin  of  the  Ores. — Corundum  and  its  varieties  occur  both  as 
primary  and  secondary  minerals.  According  to  F.  W.  Clarke 
the  most  important  experiments  from  a  geological  standpoint 
upon  the  genesis  of  corundum  have  been  conducted  by  Moroze- 
wicz.  Morozewicz  worked  indefatigably  upon  large  artificial 
magmas,  using  the  furnace  of  a  glass  factory  in  the  preparation  of 
his  melts;  and  he  found  that  whenever  the  alumina  in  comparison 
with  the  other  bases  exceeded  a  certain  ratio,  the  excess  upon 
cooling  crystallized  out  completely  as  corundum,  as  spinel,  as 
sillimanite,  or  as  iolite,  dependent  upon  percentages.  Previous 
to  the  appearance  of  Morozewicz's  memoir,  corundum  was  not 
supposed  to  be  a  pyrogenic  mineral  but  a  product  of  contact 
matamorphism,  especially  in  limestones.  (See  Fig.  116.) 

According  to  J.  H.  Pratt  corundum  occurs  in  North  Carolina 
and  Georgia  as  a  pyrogenic  mineral  from  the  fractional  crystal- 
lization of  a  peridotite  magma,  rich  in  the  ferromagnesian  mineral 
olivine.  Corundum  has  been  observed  as  a  primary  mineral  in 
both  pegmatites  and  syenites,  but  these  occurrences  are  rare. 

Corundum,  of  secondary  origin,  is  a  product  of  contact 
metamorphism  and  is  generally  associated  with  shales  and  lime- 
stones. Emery  is  perhaps  best  regarded  as  a  variety  of  corundum. 
It  consists  of  corundum  admixed  with  hematite,  magnetite,  and 
sometimes  spinel. 

The  hydrous  oxides,  diaspore  and  gibbsite  are  often  formed  by 
the  hydration  of  corundum.  Bauxite,  according  to  C.  W.  Hayes 
belongs  to  the  hot  spring  deposits.  Percolating  meteoric  waters 
have  converted  pyrite,  the  sulphide  of  iron,  into  melanterite, 


220  ECONOMIC  GEOLOGY 

the  green  sulphate  of  iron.  During  the  process  the  sulphuric 
acid  has  attacked  the  alumina  in  the  shales.  These  solutions 
traversing  limestones  would  find  the  calcium  carbonate  reacting 
upon  the  aluminum  sulphate  solutions  according  to  the  equation 


The  gelatinous  precipitate  thus  formed  is    carried   upward  in 
spring  basins  where  it  finally  settles  as  a  pisolitic  mineral.     In 


FIG.  116. — Map  showing  the  occurrence  of  corundum  as  a  differentiation 
product  of  peridotite.  (After  Thomas  and  MacAlister's  Geology  of  Ore 
Deposits.) 

the  absence  of  the  calcium  carbonate  to  react  upon  the  hydrous 
sulphate  of  aluminum  the  alums  would  be  formed  in  the  above 
process  of  alteration.  Waters  containing  the  sulphates  of  iron 
and  aluminum  form  deposits  of  these  salts  in  close  proximity  to 
their  points  of  origin.  They  are  commonly  found  as  stalactites 
and  even  as  incrustations.  Alunite  and  alunogen  are  the  com- 
monest species  thus  generated.  They  are  found  around  mineral 
springs  and  in  the  shafts  or  tunnels  of  mines. 

The  silicates  of  aluminum  occur  both   as  primary  and   as 


USEFUL  METALS 


221 


secondary  minerals  but  their  discussion  belongs  with  the  non- 
metallics. 

Character  of  the  Ore  Bodies. — Corundum  occurs  as  oval  or 
lenticular  ore  bodies  near  the  margin  of  peridotites  or  norites. 
They  differ  in  many  respects  from  those  formed  by  the  thermal 
metamorphism  of  sediments.  There  is  usually  a  complete  ab- 
sence of  such  metamorphic  minerals  as  cyanite,  which  plays  an 
important  part  in  the  corundum  deposits  of  Siam  where  the  ore 
is  a  product  of  metamorphism.  In  the  case  of  the  peridotites 
the  alumina  was  dissolved  in  the  original  magma  at  the  time  of 


FIG.  117. — View  of  Bauxite  bank,  Rock  Run,  Alabama.     (By  permission  of 
the  Macmillan  Company,  from  Ries'  Economic  Geology.) 

its  intrusion  into  the  country  rock  and  then  separated  forming 
lens-shaped  masses  at  an  early  stage  as  the  magma  began  to  cool. 

Alumina  is  also  soluble  to  some  extent  in  molten  magnesium  sili- 
cates, and  if  the  magma  has  no  excess  of  magnesium  all  the 
aluminum  will  crystallize  as  corundum,  but  if  there  be  a  slight 
excess  of  magnesium  over  that  required  for  the  magnesium  sili- 
cates then  spinel  will  be  formed. 

Corundum  occurs  as  a  contact  deposit  between  some  intrusive 
and  limestones  or  shale.  In  Massachusetts  at  Chester  corundum 
and  emery  occur  in  a  large  vein  consisting  mainly  of  emery, 


222  ECONOMIC  GEOLOGY 

magnetite  and  diaspore,  in  association  with  repidolite  and  marger- 
ite,  and  traversing  metamorphics. 

Rubies  occur  in  situ  in  the  limestones  of  Upper  Burma,  north 
of  Mandalay,  also  in  the  soils  upon  the  adjacent  hillsides  and  in 
the  gem-bearing  gravels  of  the  valleys.  Gem  sapphires  are  found 
near  Helena,  Montana,  in  the  gold  washings  and  in  the  various 
bars  in  the  Missouri  River. 

Bauxite  occurs  in  pockets  or  lenses  of  variable  length  and 
breadth  (Fig.  117).  It  may  be  either  pisolitic  or  clay-like  in 
structure,  white  or  red  in  color.  All  of  the  red  varieties  are  rich 
in  iron.  Gibbsite  in  Arkansas  is  of  the  granitic  type  and  rests 
upon  a  bed  of  clay  derived  from  an  elaeolite  syenite,  from  which 
also  the  gibbsite  was  probably  derived.  The  alums  occur  as 
incrustations  and  sometimes  as  stalactites  around  mineral  springs 
and  at  the  entrance  to  mines. 

Cryolite  occurs  in  a  large  bedded  deposit  in  Greenland  which 
F.  Johnstrup  regards  as  a  concretionary  secretion  in  eruptive 
granite.  Cryolite  is  found  sparingly  in  the  granites  of  Pikes 
Peak,  Colorado,  and  at  Miask  in  the  Ural  Mountains. 

Geographical  Distribution. — There  are  many  scattered  occur- 
rences of  corundum  and  its  associated  minerals  along  the 
Appalachian  belt  from  Dudleyville,  Alabama,  to  Greenwood, 
Maine.  The  mines  of  the  greatest  commercial  significance  are 
located  at  Laurel  Creek,  Georgia,  and  Corundum  Hill,  North 
Carolina.  It  occurs  at  Unionville,  Pennsylvania,  in  masses 
weighing  4,000  Ib.  Here  it  is  associated  with  tourmaline,  mar- 
gerite  and  albite.  The  deposits  at  Chester,  Massachusetts, 
have  been  operated  for  a  considerable  period  of  time  in  the  manu- 
facture of  the  well  known  Chester  emery.  Emery,  magnetite 
and  diaspore  enter  into  the  finished  product,  under  the  name  of 
emery.  Probably  the  largest  deposits  of  emery  in  the  world  are 
found  on  the  Island  of  Naxos  in  the  Grecian  Archipelago  and  in 
Asia  Minor  where  the  ore  deposits  are  supposed  to  be  the  prod- 
uct of  metamorphism. 

There  are  five  distinct  districts  of  commercial  bauxite  in  the 
United  States.  (1)  Wilkinson  County,  Georgia,  district;  (2) 
Georgia- Alabama  district;  (3)  Tennessee  district;  (4)  Arkansas 
district;  and  (5)  New  Mexico  district. 

(1)  According  to  A.  C.  Veatch  commercial  bauxite  occurs  in 
Wilkinson  county,  Georgia,  near  the  margin  of  the  Coastal  Plain. 
The  beds  have  a  maximum  thickness  of  10  ft.  and  lie  near  the  con- 


USEFUL  METALS 


223 


tact  of  the  Lower  Cretaceous  and  Tertiary  formations.  The  ores 
are  generally  pisolitic  or  concretionary,  but  sometimes  they  are 
amorphous  and  flinty.  Veatch  considers  that  the  ore  was  formed 
by  a  desilicification  of  the  kaolinite  in  the  associated  clays  by  cir- 
culating meteoric  waters  carrying  some  chemical  capable  of  ex- 
tracting the  silica  from  the  hydrous  aluminum  silicate  (Fig  117). 
(2)  In  the  Georgia-Alabama  district  the  bauxite  deposits  ex- 
tend from  Cartersville,  Georgia,  to  Jacksonville,  Alabama,  a  dis- 
tance of  about  60  miles  (see  Fig.  118).  They  are  found  at  altitudes 


,du 


FIG.  118. — Geologic  map  of  Alabama — Georgia  bauxite  region.  After 
Hayes.  (By  \permission  of  the  Macmillan  Company,  fromRies1  Economic 
Geology.} 

varying  from  850  to  950  ft.  above  sea  level.  The  ores  are  pisolitic, 
or  clay-like.  They  form  pockets  or  lenses  of  variable  breadth 
and  thickness  in  the  residual  clays  derived  from  the  underlying 
limestone.  According  to  C.  W.  Hayes  the  bauxite  belongs  to  the 
hot  spring  deposits.  The  Connasauga  shales  underlying  the 
Knox  dolomite  are  thousands  of  feet  in  thickness  and  bear  pyrites. 
Percolating  meteoric  waters  acting  upon  the  sulphide  of  iron  pro- 
duced sulphuric  acid.  The  sulphuric  acid  attacked  the  aluminif- 
erous  shales  forming  the  sulphates  of  iron  and  aluminum.  These 
solutions  were  transported  upward  through  the  Knox  dolomite 


224  ECONOMIC  GEOLOGY 

where  the  calcium  compounds  in  the  dolomite  produced  alumina 
amd  calcium  sulphate.  The  aluminum  compound  which  was 
light  and  gelatinous  was  carried  upward  into  spring  basins  on  the 
surface  where  it  finally  settled. 

(3)  The  bauxite  deposits  of  the  Tennessee  district  are  situated 
near  Chattanooga,  on  the  southeast  slope  of  Missionary  Ridge. 
They  came  into  prominence  in  1907.     According  to  H.  Ries  they 
represent   the   northward   extension   of   the    Georgia-Alabama 
district. 

(4)  The  bauxite  deposits  of  Arkansas  are  confined  to  a  small 
area  in  Pulaski  and  Saline  Counties.     These  ores  have  been  care- 
fully studied  by  C.  W.  Hayes,  J.  C.  Branner,  and  J.  F.  Williams, 
who  state  that  the  ores  are  found  in  Tertiary  areas  in  the  neighbor- 
hood of  irruptive  syenites  and  in  a  region  free  from  limestones. 
There  are  two  varieties  of  the  ore.     The  one  is  granitic,  and  the 
other  pisolitic.     The  granitic  variety  shows  the  structure  of  the 
syenite  from  which  it  was  probably  derived.     The  pisolitic  variety 
was  doubtless  deposited  from  solution.     The  three  authorities 
agree  in  tracing  the  genesis  of  the  bauxite  back  to  the  action  of 
waters  upon  the  heated  syenite.     Hayes  believes  that  these 
waters  were  either  alkaline  or  saline,  that  they  dissolved  out  the 
silica  and  the  alkalis  and  deposited  alumina  in  their  places. 
Fourche  Mountain,  which  constitutes  one  of  the  bauxite  areas,  is 
the  home  of  elaeolite  syenite  and  both  diaspore  and  gibbsite  are 
recognized  as  decomposition  products  of  elaeolite  and  sodalite. 

According  to  F.  W.  Clarke,  bauxite  is  intermediate  between 
diaspore  and  gibbsite  and  represents  an  admixture  of  the  two 
hydrates,  sometimes  approaching  one  in  composition  and  some- 
times the  other.  The  granitic  type  above  referred  to  very  closely 
conforms  to  gibbsite,  while  the  pisolitic  type  may  more  nearly 
represent  A12O3,2H2O.  One  variety  of  the  bauxite  is  high  in  silica 
and  low  in  iron,  while  the  other  has  been  worked  as  an  iron  ore 
on  account  of  its  high  percentage  of  iron. 

(5)  Bauxite  deposits  occur  in  the  vicinity  of  Silver  City,  New 
Mexico,  which  appear  to  have  been  derived  from  a  basic  volcanic 
rock  in  situ.     These  ore  bodies  are  some  distance  from  the  rail- 
road and  therefore  are  not  extensively  worked. 

The  type  locality  for  bauxite  is  the  town  of  Baux  in  the  south- 
ern part  of  France.  It  is  from  this  district  that  the  mineral  de- 
rives its  name.  At  Baux  the  ore  occurs  in  irregular  masses  in 
Cretaceous  limestones  where  it  has  been  deposited  through  the 


USEFUL  METALS  225 

agency  of  mineral  springs.  The  action  which  brought  about  the 
precipitation  was  doubtless  metasomatic  and  dependent  upon  the 
limestone. 

According  to  Thomas  and  MacAlister  metasomatic  bauxite 
deposits  occur  in  the  Puy  de  Dome  district  of  Central  France, 
and  in  the  northern  part  of  Ireland  in  association  with  basaltic 
rocks  from  which  they  were  evidently  derived. 

Geological  Horizon. — The  ores  of  aluminum  are  not  confined 
to  the  rocks  of  any  particular  age.  Corundum  and  emery  are 
more  abundant  in  the  older  geological  formations  as  the  pre- 
Cambrian,  Cambrian  and  Ordovician.  The  bauxite  deposits  of 
Arkansas  are  in  part  as  late  as  the  Tertiary. 

Methods  of  Extraction. — Aluminum  was  isolated  for  the  first 
time  in  1827  by  Wohler  by  means  of  the  effect  of  potassium  upon 
the  anhydrous  chloride.  Commercially  it  has  been  obtained  in 
large  quantities  by  the  ignition  of  cryolite  with  sodium  or  potas- 
sium. Two  processes  have  been  used  to  produce  commercial 
aluminum:  The  chemical  process,  and  the  electrolytic  process. 

(1)  In  the  chemical  process  the  chloride  of  the  metal  is  fused 
with  the  double  fluoride,  cryolite,  in  the  presence  of  metallic 
sodium  or  potassium  when  elemental  aluminum  results  from  the 
reducing  action  of  the  sodium  or  potassium.     It  has  been  pro- 
duced commercially  without  the  aid  of  an  alkali  from  a  mixture 
of  clay,  cryolite,  bauxite,  with  carbon  and  carbon  disulphide. 

(2)  In  the  electrolytic  process  a  mixture  of  corundum,  cryolite 
and  bauxite  have  been  subjected  to  the  intense  heat  of  an  electric 
furnace.     A  carbon-lined  crucible  has  served  as  the  cathode  and 
a  bundle  of  carbon  rods  as  the  anode.     The  metallic  aluminum 
collects  at  the  bottom  of  the  crucible. 

Uses  of  Aluminum. — Aluminum  is  used  in  many  forms  in  the 
minor  as  well  as  the  grosser  industries,  in  articles  useful,  or 
luxurious.  It  is  used  in  the  manufacture  of  keys,  visiting  cards, 
pocket  calenders,  thimbles,  brushes,  combs,  letter  cases,  cigar 
cases,  cigarette  cases,  for  which  the  metal  is  highly  valued  on 
account  of  its  extreme  lightness. 

It  is  used  in  the  manufacture  of  opera  glasses,  spectacles, 
knives,  watches,  and  many  articles  of  adornment.  It  finds  a 
use  in  household  utensils  such  as  cups,  saucers,  plates,  chafing 
dishes,  tea  urns,  etc.  It  is  used  in  individual  communion  sets,  also 
in  the  manufacture  of  a  large  number  of  toys.  It  is  utilized  in 
the  alums  in  medicine.  It  is  used  in  the  springs  in  shoes.  Alum- 

15 


226  ECONOMIC  GEOLOGY 

inum  is  used  in  the  manufacture  of  camp  equipment,  where  special 
lightness  and  non-corrosiveness  are  desirable.  The  metal  is 
used  also  in  the  manufacture  of  army  equipments  as  shells  for 
cartridges,  drum  heads  for  the  Austrian  army.  It  was  tried  in 
drum  heads  in  the  United  States  during  the  Spanish-American 
war,  but  this  use  was  not  desired  by  the  American  soldier. 

Aluminum  is  used  extensively  for  pigments.  By  the  intro- 
duction of  a  small  quantity  of  aluminum  a  paint  is  formed  which 
is  more  impervious  to  the  action  of  the  corrosive  gases  of  the 
atmosphere  or  a  laboratory  than  almost  any  other  pigment. 
The  metal  is  used  in  silvering  letters  and  signs. 

Aluminum  is  used  in  the  reduction  of  refractory  metals  to  the 
elemental  state.  Copper,  chromium  and  iron  are  very  readily 
reduced  to  the  metallic  state  through  the  influence  of  aluminum. 
It  is  used  also  in  lithography  where  it  displaces  limestone  and 
zinc  for  stock  patterns  for  foundry  work.  It  is  used  extensively 
for  boat  building  and  marine  engineering.  It  was  utilized  in  the 
manufacture  of  vessels  for  the  Madagascar  campaign  for  France 
and  the  vessels  were  returned  to  France  exceedingly  well  pre- 
served. Under  certain  conditions  of  cleanliness  a  progressive 
disintegration  of  the  metal  can  occur.  In  England  aluminum 
was  not  generally  adopted  for  the  army.  In  India  the  govern- 
ment adopted  the  metal  for  this  work  in  1902.  The  report  of 
the  German  Admiralty  authorities  was  that  aluminum  remains 
unattacked  in  the  presence  of  both  air  and  sea  water.  It  is  used 
in  light  boat  building.  The  international  racing  yachts,  the 
Columbia  and  the  Shamrock,  each  contained  large  quantities  of 
aluminum.  The  Shamrock  was  lined  with  aluminum  to  the 
water  line.  The  deck  plating  and  the  top  staff  were  also 
aluminum. 

The  numerous  uses  of  aluminum  in  metallurgy,  whether  in  the 
form  of  the  metal  or  in  a  pulverulent  state,  depend  upon  its 
remarkable  affinity  for  oxygen  and  its  power  to  rob  all  other 
metals  of  this  element  when  in  contact  with  them  under  the 
right  condition  of  heat. 

In  1901  the  United  States  purchased  10,000  blanks  the  size  of 
a  nickel  presumably  for  coinage.  Such  coins  would  be  light  and 
should  wear  well.  Aluminum  is  used  in  the  New  York  telegraph 
and  telephone  wires.  These  have  stood  the  ravages  of  many 
winters  without  failure.  It  is  used  extensively  for  such  pur- 
poses in  high  altitudes  where  the  snows  are  heavy  and  deep. 


USEFUL  METALS  227 

The  specific  heat  of  aluminum  melts  the  snow  as  it  falls  upon 
the  wire,  therefore  the  wires  do  not  stretch  and  break  under 
the  burden  of  the  snow  like  copper  wire  The  electrical 
conductivity  of  aluminum  is  double  that  of  copper  per  pound, 
therefore  it  has  a  superior  advantage  for  electrical  purposes 
wherever  the  wires  are  subject  to  severe  storms. 

The  general  post-office  authorities  of  England  have  intro- 
duced aluminum  into  their  long-distance  communications.  The 
large  increase  in  the  domestic  consumption  of  the  metal  is  largely 
due  to  the  use  of  aluminum  for  electrical  conductors,  and  the 
ease  with  which  it  replaces  zinc  in  brass.  The  electric  lines  in 
Chicago  have  in  part  substituted  aluminum  wires  for  copper 
and  these  are  giving  perfect  satisfaction. 

Among  the  newer  uses  of  aluminum  is  that  for  the  production 
of  intense  heat  by  the  combustion  of  the  metal  in  the  form  of 
the  powder  called  thermit,  which  is  the  base  of  three  important 
branches  of  metallurgy.  It  is  used  in  the  manufacture  of  a 
special  explosive  called  amonal.  It  is  used  in  the  rubber  in- 
dustry for  making  lasts  and  boot  trees  upon  which  rubber  boots 
and  shoes  are  manufactured.  It  is  used  as  a  substitute  for 
wood  in  making  bobbins  for  spinning  and  revolving  machinery 
used  in  the  manufacture  of  silk  fiber.  It  is  used  as  a  substitute 
for  glass  and  many  forms  of  earthern  ware,  in  carboys  employed 
for  the  transportation  of  nitric  acid,  as  a  substitute  for  zinc  in 
the  linings  of  cisterns  and  other  receptacles  for  storing  water. 

Aluminum  alloys  readily  with  other  metals  both  common  and 
rare,  and  furnishes  many  useful  alloys.  The  number  of  these 
light  alloys  now  upon  the  market  is  large.  The  metal  itself  is  so 
soft  when  produced  by  electrolytic  methods  that  some  hardening 
element  is  very  desirable.  Silicon  possesses  this  factor  whether 
present  accidentally  or  added  intentionally.  If  more  than  2  per 
cent,  silicon  is  present  it  impairs  the  malleability  of  aluminum 
but  does  not  diminish  its  value  in  castings.  Aluminum  bronze 
containing  10  per  cent,  or  less  of  aluminum  is  largely  used  in 
the  arts.  It  is  commercially  used  as  aluminum  gold.  As  it 
contains  no  tin  it  is  not,  strictly  speaking,  a  bronze.  Bronze 
with  5  per  cent,  aluminum  closely  resembles  pure  gold.  With 
10  per  cent,  aluminum  the  alloy  is  a  little  darker  than  22.  carat 
gold.  With  a  larger  percentage  of  aluminum  the  alloy  whitens. 
With  more  than  15  per  cent,  aluminum  the  alloy  becomes  white. 

Many  of  the  aluminum  alloys  have  a  tensile  strength  ranging 


228  ECONOMIC  GEOLOGY 

from  83,000  to  91,000  Ib.  per  square  inch.  One  alloy  is  said  to 
have  a  tensile  strength  of  over  100,000  Ib.  per  square  inch. 
Aluminum  bronze  can  be  rolled  into  thin  sheets,  readily  drawn 
out  into  wire,  spun,  stamped,  or  pressed  like  ordinary  brass. 
It  is  extremely  tough  and  malleable.  Its  smoothness  enables 
it  to  resist  abrasion  so  that  it  is  adapted  for  use  as  an  anti- 
friction metal.  It  resists  corrosion  far  better  than  the  bronzes 
and  tarnishes  less  readily  upon  exposure  to  moist  atmosphere. 
According  to  Sexton  it  can  be  kept  at  a  red  heat  for  months 
without  showing  any  signs  of  oxidation.  The  alloy  is  well 
adapted  for  use  in  jewelry  on  account  of  its  color,  and  for  many 
parts  of  machinery  on  account  of  its  tensile  strength,  for  propeller 
blades  for  ships  on  account  of  its  strength  and  non-corrosiveness, 
and  for  the  castings  of  heavy  guns  on  account  of  its  strength. 
The  strongest  aluminum  alloy  known  is  said  to  consist  of  27  per 
cent,  copper,  10  per  cent,  aluminum  and  3  per  cent,  silicon. 
Many  alloys  of  aluminum  containing  10  per  cent,  or  less  of  copper 
are  widely  used  where  lightness,  strength  and  non-corrosiveness 
are  desired.  Magnalium  is  an  alloy  of  aluminum  with  mag- 
nesium. It  is  lighter  than  pure  aluminum  with  specific  gravity 
of  2.4.  It  is  ductile  and  malleable.  It  can  be  spun,  drawn  or 
forged  like  aluminum.  It  is  non-corrodible  and  has  a  tensile 
strength  of  42,000  Ib. 

Ferro-aluminum  is  an  alloy  of  aluminum  and  iron  used  largely 
in  the  manufacture  of  steel.  It  is  a  yellowish  white  alloy,  hard 
and  brittle.  Aluminum  unites  with  tin  in  the  formation  of  a 
series  of  useful  alloys  especially  for  optical  instruments  in  the 
place  of  brass.  These  alloys  can  be  used  in  the  place  of  aluminum 
wherever  lightness  is  desired.  Aluminum  and  zinc  form  impor- 
tant alloys.  If  a  small  amount  of  aluminum  be  added  to  zinc  it 
renders  the  metal  more  fluid.  It  therefore  increases  the  area  a 
given  amount  of  zinc  will  galvanize.  It  also  reduces  the  amount 
of  oxidation  that  may  occur.  With  18  per  cent,  of  zinc  the  alloy 
is  easily  worked  and  of  technical  value.  Aluminard  is  an  alloy 
of  copper,  nickel,  zinc,  and  phosphorus.  It  takes  a  polish  equal 
to  aluminum  and  is  used  in  the  castings  for  delicate  machinery. 
Partinium  is  a  new  alloy  patented  at  Putaux,  France.  It  is 
designed  for  the  bodies  of  steam  omnibuses,  bearings  of  engines 
and  shop  shaftings.  .Aluminite  is  a  fire-proof  flooring  used 
extensively  in  kitchens,  halls  and  grill  rooms.  It  makes  a  light 
soft  flooring. 


USEFUL  METALS  229 

Bauxite  is  used  in  the  manufacture  of  aluminum,  aluminum 
sulphate,  alums,  etc.,  and  in  the  linings  of  furnaces  on  account  of 
its  refractoriness.  The  low  ocean  freight  rates  from  foreign 
ports  allow  bauxite  to  be  delivered,  duty  included,  from  the 
southern  part  of  France  to  New  York,  Philadelphia,  or  Baltimore, 
at  a  lower  rate  than  it  costs  to  ship  bauxite  from  Alabama, 
Georgia,  or  Arkansas  to  Philadelphia.  French  bauxite  can  be 
delivered  in  Philadelphia  at  $0.55  per  ton  cheaper  than  the 
American  bauxite  can  be  supplied  to  the  same  market  and  in 
Boston  for  $1.70  per  ton  cheaper  than  the  home  product  can  be 
delivered  in  the  same  city.  One  reason  for  the  advantage  the 
French  bauxites  have  over  the  American  is  that  they  do  not 
have  to  be  quarried.  The  richest  mines  are  in  the  southern  part 
of  France  in  the  neighborhood  of  Baux,  30  miles  from  the  coast. 
Three  kinds  of  bauxite  exist  in  the  district :  Ferruginous,  spotted, 
and  aluminous.  The  demand  for  the  first  is  small  on  account 
of  its  iron  content.  The  spotted  variety  contains  21.99  per  cent, 
of  iron  oxides  and  60  per  cent,  of  the  aluminum  oxide.  The  third 
variety  is  the  one  most  sought  because  the  iron  and  silica  are 
both  low  and  the  aluminum  is  higher  than  in  the  other  varieties. 
In  order  to  carry  on  the  bauxite  industry  with  profit,  works 
should  be  established  with  modern  appliances  so  that  the  various 
salts  of  aluminum  and  the  aluminous  refractory  compounds  may 
be  manufactured. 

Cryolite  is  used  in  the  manufacture  of  hydrofluoric  acid,  the 
various  fluorides  of  commerce,  some  sodium  salts,  and  also  as  a 
source  of  aluminum.  The  fluorides  are  sold  to  smelters  and  glass 
manufacturers  except  the  sodium  fluoride  which  is  shipped 
directly  to  Europe  and  India,  and  used  in  the  manufacture  of 
opalescent  glass  which  closely  resembles  French  porcelain.  The 
glass  is  extremely  hard  and  tough  and  can  be  worked  as  easily 
as  ordinary  glass. 

The  Pennsylvania  Salt  Company  has  at  times  possessed  the 
sole  power  to  import  cryolite  into  the  United  States  and  South 
America.  The  supply  is  controlled  by  the  Danish  government. 
There  are  no  commercial  deposits  of  cryolite  in  the  United 
States,  although  it  is  found  near  Pikes  Peak,  Colorado,  and  in 
Yellowstone  National  Park.  The  value  of  the  Ivigtut  cryolite 
is  $80  per  ton,  determined  as  follows:  (1)  Cost  at  the  mine  in 
Greenland.  (2)  Royalty  to  the  Danish  government.  (3)  Ocean 
freight  rates.  (4)  Domestic  freight  rates.  (5)  Cost  of  concen- 


230  ECONOMIC  GEOLOGY 

tration.     (6)  Cost  of  grinding  and  packing  in  barrels.     (7)  Other 
minor  expenses. 

Chromium:  Its  Properties,  Occurrence  and  Uses 

Properties. — Chromium,  symbol  Cr,  is  a  hard  steel-gray 
metal  permanent  in  dry  atmosphere,  even  in  minute  quantities. 
Unlike  iron  it  is  non-magnetic.  The  magnetism  sometimes 
feebly  present  in  the  chief  ore,  chromite,  is  due  to  the  ferrous 
oxide  present  in  the  mineral.  Chromium  is  soluble  in  HC1.  It 
imparts  great  hardness  and  tenacity  to  steel.  Its  specific 
gravity  is  6.8.  Its  melting  point  is  1515°  C.  Its  atomic  weight 
is  52.1. 

Ores  of  Chromium. — The  metal  does  not  occur  free  and  un- 
combined  in  nature  on  account  of  its  affinity  for  oxygen.  The 
chromium  minerals  are  therefore  oxygenated  compounds. 

Chromite,  Cr203,FeO,  68  per  cent.  Cr.  The  ferrous  iron  may 
be  replaced  by  manganese  and  the  chromium  by  ferric  iron  and 
aluminum. 

Chrome  ocher,  Cr203.  A  bright  green  mineral  bearing  some 
clay. 

Crocoite,  PbCrC>4.  A  rare  mineral  in  varying  shades  of  hya- 
cinth red. 

The  first  mentioned  mineral,  chromite,  is  the  sole  source  of  the 
metal  of  commerce.  It  is  widely  diffused  in  the  basic  igneous 
rocks  rich  in  magnesium.  It  has  been  found  in  placers  derived 
from  their  decomposition.  It  has  been  observed  adherent  to 
an  interpenetrating  platinum  magnet.  The  rare  mineral, 
daubreelite,  Cr2S3,FeS,  has  been  observed  in  several  meteorites. 

Origin  of  the  Ores. — S.  Meunier  has  suggested  that  whenever  an 
alloy  of  chromium  anol  iron  is  brought  up  from  the  zone  of 
flowage  it  oxidizes  as  it  nears  the  surface.  The  theory  is 
objectionable  because  no  such  alloy  is  known  to  exist  in  nature. 
Chromite  is  essentially  a  primary  magmatic  mineral.  It  is  one 
of  the  first  minerals  to  segregate  from  an  ultra-basic  magma 
like  peridotite.  Its  associate  in  this  differentiation  is  magnetite. 
Microscopic  slides  of  the  magnetites  and  chromites  of  northern 
Vermont  and  Megantic  County,  Quebec,  have  been  prepared  to 
ascertain  which  of  these  ores  solidified  first  but  the  problem  is 
still  unsolved.  Ore  bodies  sufficiently  large  to  be  of  commercial 
significance  are  definitely  recognized  as  a  product  of  magmatic 


USEFUL  METALS  231 

differentiation  in  northern  Vermont  and  Megantic  County, 
Quebec.  The  mines  in  the  Canadian  territory  are  still  worked, 
but  those  in  Vermont  are  idle,  although  a  considerable  amount 
of  ore  was  at  one  time  mined  in  the  town  of  Troy.  The  larger 
ore  bodies  of  Pennsylvania  lie  in  the  same  peridotite  belt  and 
possess  the  same  mode  of  origin.  J.  H.  Pratt  has  assigned 
magmatic  segregation  to  the  chromite  deposits  of  the  southern 
Appalachians.  Chrome  ocher  may  result  from  the  alteration 
of  chromite. 

Character  of  the  Ore  Bodies. — Chromite  occurs  in  irregular 
pockets,  veins,  and  lens-shaped  masses  segregating  near  the 
periphery  of  a  peridotite  magma.  It  is  also  found  in  placers  in 
association  with  platinum  where  it  has  been  derived  through  the 
decomposition  of  peridotite. 

Geographical  Distribution. — There  are  two  distinct  belts  of 
chrome  iron  ore  in  the  United  States:  The  Appalachian  dis- 
trict and  the  California  district. 

The  first  of  these  districts  may  be  subdivided  into  three  dis- 
tinct fields.  The  southern  lies  in  north  Carolina  and  Maryland; 
the  central  has  reached  its  best  development  in  Pennsylvania 
and  the  third  in  northeastern  Vermont  and  Canada.  Deposits 
of  chromite  occur  in  the  western  part  of  North  Carolina  and 
in  Baltimore  County,  Maryland,  but  these  ores  are  no  longer 
worked.  The  Wood's  mine  in  Lancaster  County,  Pennsylvania, 
was  opened  in  1828  and  worked  continuously  until  1869,  when  the 
mine  filled  with  water.  At  one  time  this  mine  produced  practic- 
ally all  the  chromite  in  the  world.  The  ore  was  also  worked  at 
one  time  in  Chester  and  Delaware  Counties,  but  these  mines  have 
also  been  abandoned.  Chromite  ores  were  worked  in  the  early 
60's  in  the  northeastern  part  of  Vermont,  but  distance  from  the 
railroad  led  to  the  abandonment  of  these  mines  also.  In  Megan- 
tic  County,  Quebec,  and  in  Newfoundland  where  the  ores  occur 
in  the  same  peridotite  belt  they  are  still  extensively  mined. 

In  the  California  district  the  deposits  of  chromite  reach  their 
best  development  in  San  Luis  Obispo  and  Shasta  Counties.  In 
the  former  county  the  mines  like  those  of  the  Appalachian  belt 
have  been  abandoned.  The  ores  of  Shot  Gun  creek  in  the  latter 
are  still  worked  for  their  chrome  content.  According  to  H.  Ries 
the  ore  occurs  in  serpentine  in  a  series  of  five  lenses,  each  contain- 
ing from  200  to  1500  tons  of  chromite.  Each  lens  is  connected  by 
vein-like  stringers  in  a  nearly  vertical  shear  zone.  The  ore  con- 


232  ECONOMIC  GEOLOGY 

tains  43.87  per  cent,  of  chromic  oxide.  In  1908  an  important 
deposit  of  chromite  was  discovered  in  Converse  County,  Wyoming. 

The  most  important  chromite  deposits  of  the  world  are  found 
in  Asia  Minor.  According  to  Thomas  and  MacAlister  the  ore 
exists  as  stocks  or  dike-like  masses,  and  ultra-basic  patches  in 
serpentine  formed  from  the  alteration  of  peridotite.  Similar 
deposits  exist  in  the  neighborhood  of  Kraubat,  in  Upper  Styria. 
It  occurs  also  in  a  fairly  fresh  peridotite  in  Norway.  In  New 
Caledonia,  deposits  are  commercially  increasing  in  importance. 
The  deposits  of  chromite  in  Southern  Rhodesia  are  peculiarly 
interesting,  for  they  are  associated  with  platinum  in  small  pro- 
portions with  the  sulphides  of  cobalt  and  nickel. 

Geological  Horizon. — Chromite  is  confined  in  its  workable  ore 
bodies  to  the  pre-Cambrian,  Cambrian  and  Ordovician  deposits. 
Therefore  its  association  is  with  the  older  ultra- basic  intrusives. 

Methods  of  Extraction. — The  electrolytic  method:  The  ore 
is  crushed  and  fashioned  into  a  large  crucible  where  its  complete 
electrolytic  reduction  requires  one  hour.  The  only  manufacturers 
of  chromium  in  this  country  are  the  Baltimore  Chrome  Works  at 
Baltimore,  Maryland,  and  the  Kalion  Chemical  Works  at  Phila- 
delphia, Pennsylvania.  Much  of  the  ore  treated  at  Baltimore 
comes  from  Scotland,  and  for  Philadelphia  from  Quebec  and 
Newfoundland. 

Uses  of  Chromium. — Raw  chromite  is  used  in  the  manufacture 
of  refractory  brick.  These  bricks  are  used  for  lining  basic, 
open-hearth  furnaces  in  the  steel  industry  and  as  a  hearth  lining 
for  water-jacket  furnaces  in  modern  copper  smelting.  Its 
merits  are  as  follows:  It  is  infusible;  it  does  not  become  friable 
when  heated  and  cooled;  is  unaffected  by  sudden  heating  and 
rapid  cooling;  is  not  affected  by  the  products  formed  in 
the  fusion  of  copper  ores;  it  wears  away  very  slowly  under  the 
flow  of  the  molten  metal.  Its  use  should  continue  to  increase, 
for  the  life  of  the  brick  is  many  times  greater  than  that  of  any 
other  refractory  linings  and  bottoms  in  the  iron  or  copper  in- 
dustries. This  use  has  been  thoroughly  tested  in  the  water- j acket 
furnaces  both  in  New  England  and  in  Tennessee.  The  chro- 
mite deposits  therefore  of  California  should  find  extensive  use 
in  the  furnaces  for  the  treatment  of  the  various  copper  ores  in  the 
Cordilleran  section.  In  the  linings  of  one  furnace  where  raw 
chromite  was  used  over  400  heats  were  turned  out  before  the 
basic  chromite  bricks  had  to  be  repaired  or  removed.  Therefore 


USEFUL  METALS  233 

the  manufacture  of  refractory  bricks  in  various  forms,  owing  to 
its  own  refractoriness,  will  demand  a  larger  use  for  chromite 
than  the  known  American  deposits  can  supply.  Chromite  brick 
are  made  of  chromite  and  coal  tar  or  some  other  binding  material. 
They  are  superior  to  magnesite  brick  in  many  particulars. 

Chromite  is  used  as  a  mordant  in  producing  shades  of  red, 
green,  buff,  brown  and  black.  Chromium  is  used  in  the  manufac- 
ture of  the  red  and  yellow  chromates  for  commercial  trade  and  in 
electrolysis.  Some  of  the  chromates  are  used  directly  as  a  pig- 
ment. Chromium  salts  are  used  in  printing,  dyeing,  and  in  wall 
paper.  Chromium  is  also  used  as  an  oxidizing  agent  and  in  tan- 
neries. Chrome-tanned  leather  will  resist  the  heating  of  high- 
speed belts  than  any  other  leather  known.  It  will  stand  a  harder 
usage.  Chromium  is  also  used  in  the  manufacture  of  pottery. 
Some  chromium  salts  find  a  use  in  medicine. 

Chromium  is  used  in  the  manufacture  of  steel.  Here  its  spe- 
cial value  is  its  freedom  from  carbon,  and  by  its  use  steels  high 
in  chromium  and  low  in  carbon  can  be  manufactured.  Such 
steels  are  extremely  hard  and  tough,  resist  shocks  and  are  of  great 
tensile  strength.  They  are  especially  to  be  desired  wherever 
these  properties  play  an  important  part.  It  is  sometimes  stated 
that  scales  of  chromium  separate  out  and  make  such  steel  in- 
capable of  welding  and  that  only  an  adhering  union  results. 
However,  the  welded  zone  is  equally  as  strong  as  the  unbroken 
steel. 

Chromium  is  used  very  largely  in  the  manufacture  of  alloys. 
The  ferro-alloy  is  used  with  ferro-nickel  in  the  manufacture  of 
chrome  steel  for  armor  plates,  and  armor-piercing  projectiles, 
trolley  car  wheels,  crusher  jaws,  stamp  mill  shoes,  so-called 
burglar  proof  safes,  tires,  axles,  springs,  magnet  steel,  cutlery, 
mechanical  implements  and  bridge  steel. 

The  ferro-chrome  alloy  is  produced  under  the  intense  heat  of  an 
electric  furnace  from  high-grade  chrome  ores  low  in  silicon.  The 
iron,  chromium,  tungsten  and  nickel  alloy  is  especially  valuable 
for  high-speed  tools  on  account  of  its  resistance  to  heat  and 
abrasion. 

The  value  of  chromite  depends  largely  upon  the  percentage 
of  chromic  oxide,  Cr2C>3  present.  The  standard  ore  contains 
50  per  cent,  of  this  oxide.  It  increases  in  value  $1  per  ton  for  every 
unit  above  50  per  cent.  It  decreases  in  value  for  every  unit  less 
than  the  standard  50  per  cent.  When  the  percentage  of  chromic 


234  ECONOMIC  GEOLOGY 

oxide  falls  below  30  per  cent,  it  decreases  at  a  far  more  rapid  rate. 
Ores  carrying  from  40  to  50  per  cent,  of  the  oxide  are  readily 
marketable  provided  they  are  low  in  silicon.  In  spite  of  the 
value  of  the  metal  in  its  numerous  alloys  and  its  wide  application 
in  pigments  the  output  is  exceedingly  small  and  most  of  the 
ores  are  imported. 


CHAPTER  VIII 
USEFUL  METALS  CONTINUED  (GROUP  IV) 

COBALT,  NICKEL,  MANGANESE,  ZINC 
Cobalt:  Its  Properties,  Occurrence  and  Uses 

Properties. — Cobalt,  symbol  Co,  is  a  hard,  bluish-white  metal 
somewhat  suggestive  of  nickel,  but  without  its  characteristic 
yellowish  tinge.  At  a  high  temperature,  unlike  iron  and  nickel,  it 
retains  its  magnetism.  The  metal  is  malleable,  sectile,  and  very 
ductile  when  heated.  In  the  massive  form  it  is  permanent  in 
ordinary  atmosphere  but  when  in  the  pulverulent  state  it  is 
rapidly  oxidized.  Its  specific  gravity  varies  from  8.54  to  8.7. 
Its  melting  point  1530°  C.  Its  atomic  weight  is  58.97. 

Ores  of  Cobalt. — Cobalt  occurs  in  the  native  state  in  very  small 
quantities  in  meteoric  iron. 

Jaipurite,  CoS,  64.6  per  cent.  Co.  Used  in  enameling  various 
shades  of  blue  on  gold  and  silver. 

Linnceite,  Co3S4,  21.34  per  cent.  Co.  If  none  of  the  cobalt 
were  replaced  by  nickel  the  theoretical  per  cent,  of  cobalt 
would  be  57.9. 

Smaltite,  CoAs2,  28.2  per  cent.  Co.  Usually  with  some  nickel 
present. 

Safflorite,  CoAs2,  28.2  per  cent.  Co.  Nickel  and  iron  present 
in  varying  amounts. 

Skutterudite,  CoAss,  20.7  per  cent.  Co.     With  traces  of  iron. 

Cobaltite,  CoS2,  CoAs2,  35.4  per  cent.  Co. 

Erythrite  (cobalt  bloom),  3CoO,As206,8H20,  37.47  per  cent.  Co. 

Asbolite  (black  cobalt  ocher).     Composition  variable. 

Cobalt  is  widely  diffused  in  the  igneous  rocks  but  in  much 
smaller  quantities  than  its  associate  nickel.  It  is  present  also  in 
both  the  meteoric  and  terrestrial  iron.  It  has  been  found  also 
in  the  ashes  of  sea  weeds. 

Origin  of  the  Ores. — The  sulphides  of  cobalt  may  be  formed 
by  either  the  wet  or  the  dry  processes.  The  arsenides  of  cobalt 

235 


236  ECONOMIC  GEOLOGY 

according  to  F.  W.  Clarke  do  not  represent  igneous  segregations. 
They  may  have  been  leached  out  from  their  accompanying  erup- 
tive rocks,  or  may  have  been  brought  up  from  below.  The  sul- 
phate and  carbonate  of  cobalt  are  secondary  minerals.  Erythrite 
arises  from  the  oxidation  and  hydration  of  the  arsenides  and  is  a 
common  mineral  in  the  oxidized  zone  of  ore  bodies  bearing 
cobalt  as  arsenides  in  the  lower  levels.  Asbolite  is  an  alteration 
product  of  cobaltiferous  ores  and  in  many  respects  closely  resem- 
bles wad,  or  bog  manganese. 

Character  of  the  Ore  Bodies. — The  principal  ores  occur  in  well- 
defined  fissure  veins  traversing  both  intrusives  and  much-altered 
sedimentaries.  The  chief  gangue  mineral  is  calcite. 

Geographical  Distribution. — The  cobaltiferous  arsenopyrites 
are  widely  scattered  along  the  Appalachian  belt.  Analyses  of 
this  variety,  called  danaite,  from  Franconia,  N.  H.,  gave  6.45 
per  cent,  cobalt.  The  scattered  occurrences  of  nickeliferous 
minerals  in  the  Cordilleran  section  bear  cobalt. 

The  most  important  cobalt  deposits  of  America  are  found  in 
the  Province  of  Ontario,  Canada,  near  the  boundary  line  of 
Quebec  and  west  of  the  northern  end  of  Lake  Temiskaming. 
It  was  during  the  construction  of  the  Temiskaming  and  Northern 
Railroad  that  the  deposits  of  cobalt  and  silver  minerals  at  Cobalt 
were  discovered.  This  was  followed  by  a  similar  discovery  at 
South  Lorrain  and  another  at  Gowganda.  These  fields  have 
given  to  Ontario  a  position  amongst  the  leading  silver  camps  of 
the  world. 

The  geological'  section  at  Cobalt  has  as  its  base  a  series  of 
highly  folded  diabases,  granite  porphyries,  etc.,  that  are  intruded 
by  granites.  This  series  is  Kewatin  in  age.  This  series  of  ter- 
ranes  is  separated  from  the  Lower  Huronian  conglomerates  and 
slates  by  an  erosional  unconformity.  Above  the  Lower  Huronian 
rocks  is  a  series  of  conglomerates,  quartzites  and  arkoses  of 
Middle  Huronian  age.  Post-Middle  Huronian  diabases  appears 
in  sheets  and  sills.  Above  the  diabases  there  occurs  Niagara 
limestones  and  glacial  drift  completing  the  geological  section. 
The  ores  occur  in  the  conglomerates,  the  diabases  and  the  underly- 
ing Kewatin  series,  although  the  lower  formations  are  not  so 
productive  of  silver  and  cobalt. 

According  to  W.  G.  Miller  the  ores  were  deposited  by  highly 
heated  impure  waters  circulating  through  the  cracks  and  fissures 
following  the  intrusion  of  the  post-Middle  Huronian  diabase. 


USEFUL  METALS  237 

Two  possible  sources  of  the  ores  are  suggested.  (1)  The  metals 
may  have  been  brought  up  from  great  depths  by  these  waters. 
(2).  The  metals  may  have  been  leached  out  of  the  disturbed 
and  folded  Kewatin  series  of  terranes.  The  arsenides  appear  to 
have  been  the  first  minerals  deposited,  after  which  the  veins  suf- 
fered some  disturbance  which  resulted  in  the  formation  of  cracks 
and  minute  fissures  favoring  the  deposition  of  the  silver  at  a 
later  time.  A  proof  that  disturbance  preceded  the  deposition 
lies  in  the  fact  that  the  silver  cuts  the  arsenides  and  that  the 
undisturbed  veins  are  non-argentiferous.  The  veins  are  small, 
varying  from  1  in.  to  1  ft.  or  more  in  thickness.  Some  of 
them  are  of  remarkable  richness.  A  single  sample  from  the  Gow- 
ganda  camp  assayed  by  E.  E.  Burlingame  &  Co.  of  Denver, 
Colorado  gave  27,066  oz.  of  silver  per  ton  of  ore. 

Geological  Horizon. — The  commercial  deposits  of  cobaltif- 
erous  minerals  are  found  in  the  older  geological  formations  from 
the  pre-Cambrian  to  the  Ordovician. 

Method  of  Extracting. — The  ores  are  roasted,  smelted  into  a 
matte,  and  subsequently  refined  by  electrolysis. 

Uses  of  Cobalt. — Metallic  cobalt  finds  little  application  in  the 
arts  and  industries.  Cobalt  steel  has  a  high  elastic  limit  and 
tensile  strength  but  it  is  far  more  costly  to  manufacture  than  man- 
ganese or  nickel  steel  and  therefore  does  not  possess  so  wide  an 
industrial  application. 

Cobalt  is  extensively  used  as  a  pigment  in  the  manufacture  of 
glass  and  pottery.  The  beautiful  blue  color  known  as  smalt 
blue  is  imparted  to  the  glass  by  the  oxide  of  cobalt.  Zaffre,  the 
roasted  cobalt  ore,  cobalt  oxide,  arsenide,  phosphate  and  sulphate 
are  used  in  the  coloring  of  glass  and  the  painting  of  porcelain. 
Sympathetic  inks  are  made  of  cobalt  acetate  and  cobalt  nitrate. 
These  inks  are  colored  when  heated  and  colorless  when  cold.  This 
is  said  to  be  due  to  a  change  in  the  color  of  the  salts  upon  the 
absorption  of  water.  Cobalt  and  potassium  nitrate  are  used  as 
an  oil  and  water  pigment  for  painting  on  glass  and  porcelain. 
Cobalt  nitrate  is  used  in  medicine.  The  salts  of  cobalt  are  an 
antidote  for  the  deadly  prussic  acid.  The  nitrate  of  cobalt  is  also 
used  in  chemical  mineralogy  in  the  detection  of  aluminum,  tin, 
zinc  and  magnesium.  Cobalt  is  also  used  in  storage  batteries 
but  it  is  expensive  for  that  purpose.  Cobalt  is  used  in  the  manu- 
facture of  gold  and  silver  ornaments. 

The  banner  domestic  production  including  cobalt  oxide  in 


238  ECONOMIC  GEOLOGY 

ore  and  matte  came  in  1903  with  120,000  Ib.     Since  1908  the  out- 
put has  been  included  with  nickel. 

Nickel:  Its  Properties,  Occurrence  and  Uses 

Properties. — Nickel,  symbol  Ni,  is  a  lustrous  white  metal 
with  a  faintly  yellowish  tinge.  The  metal  is  ductile,  malleable 
and  sectile  but  extremely  hard  and  tenaceous.  It  is  permanent 
in  the  massive  form  in  dry  atmosphere  but  in  the  presence  of 
moisture  it  quickly  becomes  coated  with  a  film  of  the  oxide, 
NiO.  The  metal  is  magnetic  but  loses  this  property  at  high 
temperatures.  It  is  soluble  in  mineral  acids.  Its  specific  grav- 
ity when  cast  is  8.35  and  8.6  to  8.9  when  rolled.  Its  melting 
point  is  1484°  C.  Its  atomic  weight  is  58.68 

Ores  of  Nickel. — Native  nickel,  Ni,  100  per  cent.  Ni.  Often 
alloyed  with  iron. 

Millerite,  NiS,  64.6  per  cent.  Ni.  Occurring  in  capillary 
crystals  and  tufted  coatings. 

Beyrichite,  Ni3S4,  54.23  per  cent.  Ni. 

Polydimite,  Ni4S5,  59.4  per  cent.  Ni. 

Pentlandite,  (Fe,  Ni)S,  22  per  cent.  Ni. 

Pyrrhotite,  FenSn+i.     Sometimes  containing  6  per  cent,  nickel. 

Niccolite,  NiAs,  43.9  per  cent.  Ni. 

Chloanthite,  NiAs2,  28.1  per  cent.  Ni. 

Rammelsbergite,  NiAs2,  28.1  per  cent.  Ni. 

Gersdorffite,  NiAsS,  35.4  per  cent.  Ni. 

Annabergite,  3NiO,As2O5,8H20  (nickel  bloom). 

Garnierite,  (Ni,Mg)O,Si02,H20. 

Genthite,  2NiO,2MgO,3SiO2,6H2O. 

To  this  list  there  might  be  added  the  terestrial  minerals, 
awaruite,  FeNi2,  which  occurs  in  the  drift  of  George  River, 
emptying  into  Awarua  Bay  on  the  west  coast  of  the  south 
island  of  New  Zealand;  Josephenite,  FeNi2,  from  Josephine 
County,  Oregon,  and  the  nickel  alloy  FeNi3  as  found  in  the 
auriferous  sands  of  the  stream  Elvo,  near  Biella,  Piedmont, 
Italy. 

Origin  of  the  Ores. — Nickel  occurs  in  both  the  terrestrial  and 
meteoric  irons.  Some  of  these  are  best  classified  as  nickel 
alloys  for  the  percentage  of  nickel  exceeds  that  of  the  iron. 
Nickel  is  one  of  the  commonest  of  the  minor  constituents  of  the 
igneous  rocks.  According  to  F.  W.  Clarke  in  262  analyses  of 


USEFUL  METALS  239 

igneous  rocks  made  in  the  laboratory  of  the  United  States 
Geological  Survey  an  average  of  0.0274  per  cent,  nickel  oxide  was 
found.  The  sulphides  and  the  arsenides  of  nickel  may  be  formed 
by  either  the  wet  or  the  dry  processes.  Where  capillary  millerite 
appears  on  dolomite  crystals  lining  geodes  it  is  unquestionably 
crystallized  from  solution.  Where  it  occurs  as  a  radiating  in- 
crustation upon  secondary  minerals  as  in  Pennsylvania,  it  too 
must  be  of  secondary  origin  (Fig.  119). 

The  origin  of  nickeliferous  pyrrhotite  is  perhaps  an  open 
question.  According  to  J.  H.  L.  Vogt  it  represents  a  distinct 
segregation  from  a  molten  magma.  This  has  long  been  con- 


FIG.  119. — Evans  mine,  Canadian  Copper  Company,  Copper  Cliff,  Ontario. 
(After  A.   E.   Barlow,   Canadian  Geological  Survey.} 

sidered  the  origin  of  the  Sudbury,  Ontario,  pyrrhotite.  The 
order  of  segregation  has  been  most  carefully  studied  by  R.  Bell, 
H.  B.  von  Foullon,  T.  L.  Walker,  A.  P.  Coleman,  A.  E.  Barlow 
and  others.  The  order  suggested  is  chalcopyrite  near  the  wall 
rock,  then  pyrrhotite  bearing  nickel,  and  lastly  nickel  sulphide; 
the  matrix  being  norite.  According  to  D.  H.  Browne  the  occur- 
rence of  the  ores  at  Sudbury  is  comparable  to  the  phenomena 
observed  in  a  cooling  copper-nickel  matte,  in  which  the  copper 
sulphides  concentrate  along  the  margins  of  the  mass,  and  the 
nickel  sulphides  at  the  center  (Fig.  120). 

According  to  W.  Campbell  and  C.  W.  Knight  the  Sudbury 
ores  were  all  formed  from  solution.     The  order  given  is  as  follows : 


240  ECONOMIC  GEOLOGY 

First  magnetite,  then  pyrite  and  gangue,  then  pyrrhotite.  The 
mass  is  then  fractured  and  in  the  cracks  there  appears  pentlandite. 
These  ores  are  all  fractured  and  in  the  cracks  thus  formed 
chalcopyrite  is  deposited. 

According  to  F.  W.  Voit  the  nickel  ores  of  Dobschau,  Hungary, 
were  deposited  from  solution  in  a  gangue  of  calcite  at  or  near 
contacts  of  diorite.  C.  R.  Keyes  considers  the  nickel  mineral, 
linnaeite  at  Mine  La  Motte,  Mo.,  of  secondary  origin.  It 
occurs  in  limestones  as  a  metasomatic  replacement  deposit  with 
lead  and  copper.  - 


FIG.  120. — Roast  yards  near  Victoria  mine,  Mond  Nickel  Company, 
Sudbury  district,  Ontario.  (After  A.  E.  Barlow,  Canadian  Geological 
Survey.) 

The  famous  Temiskaming  mining  district  in  Ontario  was  dis- 
covered in  1903.  The  sulphides  and  arsenides  of  nickel  and  co- 
balt were  all  formed  through  solutions  from  heated  waters  asso- 
ciated with  the  basic  intrusives  of  post-Middle-Huronian  age. 
The  native  silver  of  Cobalt  and  Gowganda  was  the  last  mineral 
to  form  from  solution  in  the  ore  bodies  for  it  cuts  the  smaltite 
and  the  gangue  mineral  calcite.  According  to  W.  G.  Miller 
these  deposits  are  analogous  to  those  of  Annaberg,  Saxony,  and 
Joachimsthal,  Bohemia.  The  ores  may  represent  a  leaching  of 
the  accompanying  basic  eruptive  rocks,  or  they  may  have  been 


USEFUL  METALS  241 

brought  up  from  below.  At  all  events  they  are  not  primary 
segregations. 

Morenosite,  the  sulphate  of  nickel,  and  zaratite,  the  carbonate 
of  nickel,  are  formed  by  the  oxidation  and  carbonation  of  the 
sulphides  and  other  ores  of  the  metal. 

The  hydrous  silicates  of  nickel,  which  are  rarely,  if  ever, 
definite  mineral  species,  but  rather  a  mixture  of  the  silicates  of 
nickel  with  magnesium  compounds  and  free  silica,  are  entirely 
unlike  the  sulphides  and  arsenides  in  their  genesis.  They  form 
a  distinct  class  of  ores.  They  are  associated  with  masses  of 
serpentine  or  other  hydromagnesian  rocks.  They  represent  a 
concentration  of  the  nickel  in  a  peridotite  magma,  but  especially 
one  rich  in  nickeliferous  olivine. 

Character  of  the  Ore  Bodies. — Millerite  occurs  as  an  incrusta- 
tion upon  other  minerals  and  as  capillary  crystals  in  cavities 
among  quartz  crystals.  The  nickeliferous  pyrrhotite  occurs  as 
a  contact  deposit  between  quartzite  and  norite;  also  in  irregular 
masses  of  large  dimensions.  The  sulphides  and  arsenides  appear 
in  well-defined  fissure  veins  traversing  the  basic  intrusives  and 
their  adjacent  terranes.  Garnierite  and  genthite,  together  with 
other  hydrous  silicates  of  nickel  occur  in  enormous  deposits 
which  in  part  result  from  precipitation  and  in  part  from  the 
transition  of  a  peridotite  magma  to  serpentine. 

The  deposit  near  Noumea,  the  capital  of  New  Caledonia,  is 
perhaps  the  most  noted  nickel-bearing  ore  body  in  the  world. 
The  ores  are  particularly  free  from  sulphur,  arsenic  and  copper, 
three  constituents  injurious  to  nickel.  There  are  two  distinct 
varieties  of  these  hydrous  silicates  present.  The  one  is  green 
and  the  other  is  chocolate  brown.  The  green  variety  carries 
from  45  to  48  per  cent,  of  nickel  oxide;  the  brown  variety  carries 
from  43  to  46  per  cent,  of  the  oxide  of  nickel.  Both  contain 
small  quantities  of  cobalt.  The  green  variety  was  long  mistaken 
for  the  green  hydrous  carbonate  of  copper,  malachite.  The 
brown  variety  was  thrown  away  as  worthless  earth  which  was 
supposed  to  be  colored  by  the  hydrated  oxides  of  iron.  The 
green  variety  is  now  regarded  as  deposited  from  solution  from 
above,  while  the  brown  variety  tells  its  tale  of  the  transition  of 
the  country  rock  peridotite  to  serpentine. 

The  method  of  mining  at  Noumea  is  simply  open  cut  work. 
The  ore  is  taken  out  in  benches  having  faces  about  30  ft.  high 
so  that  the  appearance  of  the  quarry  is  not  unlike  the  risers  and 

16 


242  ECONOMIC  GEOLOGY 

treads  of  a  stairway.  The  ores  are  blended  to  a  shipping  grade, 
and  sent  to  the  lowlands  on  aerial  rope  ways,  conveyed  to  the 
coast  by  ground  trams,  transferred  to  lighters,  and  then  con- 
veyed to  ships.  The  quantity  of  ore  seems  to  be  inexhaustible. 
The  ores  are  shipped  to  England,  France,  Holland,  Germany 
and  Australia. 

Geographical  Distribution  of  Nickel. — There  are  three  distinct 
belts  of  nickel-bearing  ores  in  the  United  States:  (1)  The  Ap- 
palachian district;  (2)  the  Central  district;  and  (3)  The  Cordil- 
leran  section. 

(1)  Appalachian  belt:     But  little  nickel  has  ever  been  produced 
in  this  section.     The  largest  deposit  is  in  Lancaster  County, 
Pennsylvania,  where  the  nickeliferous  pyrrhotite  is  associated 
with  the  altered  intrusive,  amphibolite,  encased  in  mica  schist. 
J.  F.  Kemp  regards  the  amphibolite  as  an  altered  gabbro  or 
norite,  and  the  deposit  as  originally  magmatic. 

In  the  southern  Appalachian  belt  in  Webster  County,  North 
Carolina,  the  hydrous  silicates  of  nickel  appear  in  connection 
with  the  transition  of  a  peridotite  magma  (dunite)  to  serpentine. 
The  olivine  of  the  original  peridotite  bears  nickel.  The  nickel 
ore  occurs  in  small  fissures  with  talc  and  gymnite. 

(2)  Central   district    (Mo.)    comprises   the   Mine   La    Motte, 
Fredericktown  district,  which  furnishes  annually  a  small  amount 
of  nickel  as  a  by-product  from  the  lead  industry.     Nickel  was 
mined  and  smelted  to  a  small  extent  by  the  North  American 
Lead  Company. 

(3)  Cordilleran  section:  This  section  embraces  Arizona,  Idaho, 
Oregon,  Washington,  and  Wyoming,  each  of  which  have  from 
time  to  time  reported  the  existence  of  nickel-bearing  minerals, 
but  none  have  ore  bodies  that  have  yet  assumed  the  dimensions 
of  commercial  importance.     The  most  noted  of  these  occurrences 
are  those  of  Nickel  Mountain,  Oregon.     According  to  H.  Ries 
the  ore  is  genthite  associated  with  a  quartz  gangue.     It  occurs  as 
a  flat-lying  deposit  on  the  surface  of  a  post-Cretaceous,  pre- 
Eocene  peridotite,  or  as  veinlets  in  the  peridotite  and  resulting 
serpentine.     It    is    thought    that    the    genthite    represents    an 
alteration  product  of  the  peridotite,  for  nickel  has  been  found 
in  the  fresh  peridotite. 

Other  Districts. — At  Sudbury,  Ontario,  is  by  far  the  largest,  the 
best  known  and  the  most  important  nickel-bearing  ore  body  in 
America.  From  this  nickeliferous  pyrrhotite  comes  nearly  all 


USEFUL  METALS  243 

of  the  nickel  consumed  in  the  United  States.  In  fact,  practically 
the  entire  production  is  said  to  be  imported  into  the  United 
States.  However  a  small  balance  goes  to  England.  New 
Caledonia,  as  elsewhere  noted,  is  the  largest  single  producer  of 
nickel-bearing  minerals  in  the  world  (Fig.  121).  Nickel  also 
occurs  at  Revda,  southwest  of  Ekaterinburg,  in  the  Urals  nickelif- 
erous  minerals  in  connection  with  antigorite  serpentine  which 
,  is  associated  with  metamorphic  limestones  and  mica  schists; 
also  at  Frankenstein,  in  Prussian  Silesia,  in  association  also 
with  serpentine. 


FIG.  121. — Main  pit  Creighton  mine,  Sudbury  district,  Ontario.     (After 
A.  E.  Barlow,  Canadian  Geological  Survey.) 


The  association  of  the  nickeliferous  minerals  points  to  one 
thing  of  especial  interest.  Their  home  is  everywhere  shown  to 
be  connected  with  the  ultrabasic  and  basic  intrusives  a<s  perido- 
tite,  norite,  diabase  and  diorite,  rather  than  with  the  acidic 
magmas. 

Geological  Horizon. — The  important  ore  deposits  of  nickel 
are  in  the  older  geological  formations  ranging  from  the  pre- 
Cambrian  to  the  Ordovician.  The  deposits  in  Oregon  appear 
to  be  an  exception  for  they  are  associated  with  the  post-Creta- 
ceous, pre-Eocene  peridotite. 


244  ECONOMIC  GEOLOGY 

Methods  of  Extraction. — The  ore  is  first  roasted,  then  smelted 
to  a  Bessemer  matte  containing  from  77  to  80  per  cent,  of  the 
combined  metals,  copper  and  nickel,  which  is  shipped  direct  to 
the  United  States  and  Great  Britian  for  subsequent  refinement 
by  the  electrolytic  method.  Plants  exist  for  the  treatment  of 
the  Canadian  ores  at  Copper  Cliff,  Deloro,  andThorold,  Ontario. 

Uses  of  Nickel. — One  of  the  earliest  uses  of  nickel  was  in  the 
manufacture  of  German  silver,  an  alloy  of  nickel,  copper  and 
zinc.  Nickel  has  been  extensively  used  in  coinage  both  in  the 
United  States  and  in  foreign  countries.  The  standard  coin  is 
said  to  consist  of  one  part  of  nickel  and  three  parts  of  copper. 
Nickel  is  used  extensively  in  electroplating. 

Nickel  when  welded  upon  iron  and  rolled  into  sheets  is  used 
for  culinary  utensils  and  many  other  objects.  Nickel  is  used 
for  making  nickel  steel  for  heavy  machinery  and  engines;  plates, 
turrets,  and  propeller  shafts;  for  stamp  mill  shoes,  crusher  jaws, 
and  bicycles.  The  bicycle  and  the  motocycle  have  been  in  some 
measure  responsible  for  the  demand  for  nickel  in  recent  years. 
An  alloy  consisting  of  20  parts  of  nickel  and  80  parts  of  copper 
is  used  as  the  casing  of  bullets  for  small  bore  guns,  especially  in 
foreign  countries.  Europe  uses  large  quantities  of  nickel  for 
that  purpose.  Nickeloid  is  a  nickel-plated  sheet  of  zinc  which  is 
non-corrodible  and  which  is  largely  used  in  the  manufacture  of 
bath  tubs,  refrigerator  linings  and  wherever  a  metallic  surface 
is  continuously  exposed  to  moist  air  or  water.  Nickel  aluminum 
alloys  are  of  commercial  significance.  They  possess  a  tensile 
strength  exceeding  40,000  Ib.  to  the  square  inch.  New-silver 
is  an  alloy  of  nickel  and  aluminum  containing  26  per  cent,  of 
nickel.  It  is  susceptible  of  a  high  polish  and  as  its  name  implies 
so  closely  resembles  silver  that  it  cannot  readily  be  distinguished 
from  the  white  metal.  Minckin  is  a  nickel-aluminum  alloy  con- 
taining more  nickel,  and  widely  used  on  account  of  its  resistance  to 
to  the  corrosive  action  of  both  acids  and  alkalis.  Ferro-nickel 
contains  25,  35,  50,  and  75  per  cent,  of  nickel  respectively,  and 
is  manufactured  in  large  quantities  so  that  the  per  cent,  of  nickel 
required  in  steel  may  be  absolutely  controlled.  The  alloy  is 
malleable,  homogeneous,  and  may  be  either  rolled  into  plates 
or  drawn  into  wires. 

Chrome-nickel  is  utilized  in  the  manufacture  of  armor  plates 
and  armor-piercing  projectiles  which  are  superior  to  the  Harvey- 
jzed  steel  armor  plates  once  widely  utilized.  Tungsten-nickel  is 


USEFUL  METALS  245 

used  largely  in  the  manufacture  of  cutlery.  Molybdenum-nickel 
has  many  industrial  applications  and  consists  of  varying  quanti- 
ties of  the  two  metals.  As  molybdenum  is  fusible  with  difficulty 
and  hard  to  alloy  with  steel,  it  is  first  alloyed  with  nickel,  then  the 
nickel  alloy  is  alloyed  with  steel  and  used  in  the  manufacture  of 
forgings,  foundry  facings,  gun  shells,  wires,  and  boiler  plates. 
Monel  metal  contains  69  parts  of  nickel,  29  parts  of  copper  and 
two  parts  of  iron.  Its  tensile  strength  varies  from  85,000  to 
95,000  Ib.  to  the  square  inch.  The  metal  may  be  spun,  forged, 
worked  either  hot  or  cold,  and  manufactured  into  boiler  tubes  and 
sheet  metal  suitable  for  casings  where  strength  and  non-corro- 
dibility  are  desired.  The  specific  gravity  of  monel  metal  is  from 
8.94  to  8.95.  The  metal  possess  25  per  cent,  greater  tensile 
strength  and  50  per  cent,  greater  elastic  limit  than  steel.  There- 
fore the  mechanical  possibilities  of  the  alloy  are  almost  endless. 
One  of  the  most  satisfactory  uses  of  the  metal  is  in  seamless  tubes 
for  condensers  and  boilers  for  automobiles  and  motor  boats. 
The  high  elastic  limit  of  the  metal  coupled  with  its  non-corrodi- 
bility  are  of  special  value  in  light  machinery.  The  largest  casing 
yet  made  of  the  metal  is  said  to  be  the  hub  of  a  steamer  propeller. 
This  casting  is  9  1/2  ft.  in  diameter  and  weighs  6500  Ib.  The 
propellers  for  hydroplanes  are  manufactured  from  monel  metal. 

Economics. — A  few  tons  of  nickel  are  produced  annually  as  a 
by-product  in  the  treatment  of  the  lead  ores  at  Mine  La  Motte, 
Missouri.  There  are  two  companies  operating  in  the  United 
States  for  the  production  of  the  metal.  The  International  Nickel 
Company,  Bayonne,  New  Jersey,  and  the  American  Nickel 
Works,  Camden,  New  Jersey.  The  United  States  still  continues 
to  draw  its  supply  of  nickel  from  America's  most  noted  locality, 
Sudbury,  Ontario. 

In  1909  a  new  nickel  area  was  exploited  in  the  Township  of 
Dundonald  on  the  west  of  the  Temiskaming  and  Northern  Ontario 
Railway.  The  ore  is  a  Nickeliferous  pyrrhotite  closely  resem- 
bling that  of  Sudbury,  Ontario. 

Manganese :  Its  Properties,  Occurrence  and  Uses 

Properties. — Manganese,  symbol  Mn,  is  a  hard,  brittle,  steel- 
gray  metal  which  oxidizes  rapidly  on  exposure  to  moist  atmos- 
phere. It  is  readily  soluble  in  hydrochloric  acid.  The  metal 
does  not  occur  free  and  uncombined  in  nature,  and  the  refined 


246  ECONOMIC  GEOLOGY 

product  has  no  commercial  significance  save  in  its  alloys.  Its 
specific  gravity  is  8,  melting  point,  1245°  C,  and  its  atomic 
weight  is  54.93. 

Ores  of  Manganese. — Manganese  never  occurs  native  on 
account  of  its  remarkable  affinity  for  oxygen.  The  element  is 
widely  distributed  in  nature  in  somewhat  limited  quantity. 
The  oxides  and  the  hydrous  oxides  are  far  the  most  important 
minerals. 

Alabandite,  MnS,  63.1  per  cent.  Mn.  The  only  sulphide  of  the 
metals  with  an  olive  green  streak. 

Pyrolusite,  MnO2,  63.2  per  cent.  Mn.  In  pulverulent  form 
known  as  the  black  oxide  of  manganese. 

Polianite,  Mn02,  63.2  per  cent.  Mn.  Distinguished  from  pyro- 
lusite  by  its  superior  hardness  and  tetragonal  crystallization. 

Manganosite,  MnO,  74.4  per  cent.  Mn. 

Pyrochroite,  Mn(OH)  2.  The  corresponding  iron  compounds  are 
unknown  in  nature. 

Manganite,  Mn203,  H20,  62.4  per  cent.  Mn. 

Braunite,  3Mn203,  MnSi03,  69.68  per  cent.  Mn. 

Hausmannite,  Mn304,  72  per  cent.  Mn.  The  iron  equivalent  is 
magnetite. 

Psilomelane,  H4Mn06,  45  to  60  per  cent.  Mn.  With  barium 
and  potassium  variable. 

Wad.  The  formula  and  percentage  of  manganese  varies 
widely. 

Rhodochrosite,  MnC03,  61.7  per  cent.  MnO. 

Rhodonite,  MnSiO3,  54.1  per  cent.  MnO. 

The  last  two  minerals  are  pink  or  rose  colored  and  capable  of 
some  industrial  application  for  decorative  interior  work. 

Origin  of  the  Ores. — Alabandite  occurs  in  Colorado  in  asso- 
ciation with  the  carbonate  of  manganese  and  the  sulphide  of 
silver,  lead  and  iron.  The  action  of  alkaline  sulphides  upon  the 
soluble  salts  of  manganese  in  alkaline  solution  will  effect  its  pre- 
cipitation. The  mineral  is  too  rare  to  be  of  great  commercial 
significance.  It  is  used  to  a  small  extent  in  the  metallurgy  of  the 
metal. 

The  numerous  oxides  and  the  hydrous  oxides  of  manganese  are 
all  of  secondary  origin.  Forschammer  and  Dieulafait  report 
manganese  in  solution  in  oceanic  waters.  According  to  E.  Mau- 
mene*  it  occurs  in  the  ashes  oifucus  serratus.  According  to  F.  W. 
Clarke  manganese  as  an  oxide  or  hydroxide  exists  in  all  deep-sea 


USEFUL  METALS 


247 


deposits.  It  appears  as  grains  in  the  clay  or  ooze,  sometimes  as  a 
coating  upon  pumice,  coral,  shells,  or  fragments  of  bones,  often 
in  the  form  of  nodular  concretions  made  up  of  concentric  layers 
about  some  other  substance  as  a  nucleus.  Even  in  shallow 
waters,  as  in  Loch  Fyne,  in  Scotland,  these  nodules  have  been 
found,  but  they  seem  to  be  more  characteristic  of  the  deeper  ocean 
abysses,  whence  the  dredge  often  brings  them  up  in  great 
numbers. 

Some  doubt  still  exists  as  to  the  origin  of  these  manganese 
nodules.  C.  W.  Gumbel  ascribes  them  to  submarine  springs 
holding  manganese  in  solution,  which  is  precipitated  on  contact 
with  sea  water.  J.  B.  Boussingault  considers  that  the  manganese 
was  derived  from  carbonates  carried  in  solution  by  oceanic  waters. 
According  to  L.  Dieulafait  the  oxidation  of  the  carbonates  takes 


FIG.  122. — Section  in  the  manganese  region  of  north  Arkansas,  show- 
ing the  formation  of  manganiferous  clay  by  the  decay  of  the  St.  Clair  lime- 
stone. (After  Penrose.} 

place  at  the  surface  through  atmospheric  contact  after  which  the 
precipitated  oxide  falls  to  the  bottom  of  the  sea.  According  to 
J.  Murray  the  manganese  is  derived,  like  the  well-known  red  clay, 
from  the  subaqueous  decomposition  of  volcanic  debris. 

According  to  F.  W.  Clarke  the  manganese  is  derived  from 
rock  fragments  as  it  is  by  weathering  on  the  land.  It  goes  into 
solution  as  a  carbonate,  is  oxidized  by  the  dissolved  oxygen  of  the 
sea  water,  and  precipitated  near  its  point  of  derivation  around  any 
nuclei  that  may  happen  to  be  at  hand.  These  nodules  occur  in 
close  association  with  altered  volcanic  materials,  and  most  abun- 
dantly in  connection  with  the  red  clay  of  similar  origin.  Their 
impurities  are  those  which  this  method  of  formation  would  lead 
one  to  expect  (Fig.  122). 

Manganese  is  almost  invariably  present  in  small  quantities  in 


248 


ECONOMIC  GEOLOGY 


the  crystalline  rocks.  (See  Fig.  123.)  It  passes  into  solution  as 
a  carbonate  or  a  sulphate  to  be  redeposited  as  a  carbonate,  oxide, 
or  hydroxide  under  varying  conditions  and  in  a  variety  of  forms. 
The  dioxide,  hydrous  or  anhydrous  is  very  common  and  is  often 
seen  in  dendritic  infiltrations  so  abundant  in  the  sericite  schists 
of  Newbury,  Vermont,  and  elsewhere.  It  is  sometimes  observed 
as  a  black  coating  on  river  pebbles  and  on  the  various  rocks  sur- 
rounding manganiferous  mineral  springs.  M.  Thresh  cites  small 
hard  black  nodules  closely  resembling  seeds  in  the  bowlder  clays 
of  Essex,  England.  Similar  bodies  have  been  found  by  W.  M. 
Doherty  on  the  surface  of  the  ground  in  Australia. 

The  dioxides,  pyrolusite  and  polianite,  together  with  psilome- 
lane  are  the  most  important  ores  in  the  metallurgy  of  manganese. 
The  two  former  minerals  have  no  analogue  among  the  compounds 
of  iron  while  the  latter  is  a  colloidal  complex  closely  resembling 


FIG.  123. — Lens-shaped  masses  of  manganese  ores  interbedded  with  sedi- 
mentary rocks. 

some  of  the  sedimentary  ores  of  iron.  F.  R.  Mallet  has  observed 
pyrolusite  and  psilomelane  as  an  integral  portion  in  some  of  the 
Indian  laterites.  O.  A.  Derby  regards  the  manganese  ores  of 
Queluz,  Brazil,  as  residual  deposits  derived  from  rocks  in  which 
the  manganese  garnet  was  the  most  constant  and  characteristic 
silicate. 

Wad,  or  bog  manganese,  is  dissolved  from  the  various  rocks  in 
the  same  manner  as  bog  iron  and  redeposited  under  similar  con- 
ditions. Bog  manganese  usually,  if  not  always,  bears  varying 
quantities  of  iron  and  bog  iron  quite  frequently  carries  manganese. 

Character  of  the  Ore  Bodies. — In  the  United  States  the  manga- 
nese ores  occur  in  lenticular  masses,  stringers,  pockets,  grains  and 
nodules  (Fig.  124).  The  Brazilian  ores  most  nearly  correspond 
to  a  bedded  deposit. 

H.  Ries  makes  a  four-fold  division  of  the  manganese  ores  as 


USEFUL  METALS 


249 


follows:  (1)  Manganese  ores.  (2)  Manganiferous  iron  ores. 
(3)  Manganiferous  silver  ores.  (4)  Manganiferous  zinc  residuum. 
The  manganese  ores  proper  comprise  the  high-grade  pyrolusite 
and  polianite  that  are  reasonably  free  from  iron.  The  Brazilian 
ore,  psilomelane,  meets  this  demand  as  will  be  seen  later  in  the 
discussion  of  its  composition. 

The  manganiferous  iron  ores  consist  largely  of  limonite  and 
hematite  bearing  certain  quantites  of  pyrolusite,  psilomelane,  or 
even  wad.  The  higher  grade  ores  of  this  class  find  use  in  the 


FIG.  124. — Section  exposed  in  a  pit  in  the  Dobbins  mine  in  Georgia. 
The  black  bands  represent  manganese  ore  and  the  shaded  portion  clays. 
(After  Penrose.) 

manufacture  of  f erromanganese  and  spiegeleisen  for  the  manufac- 
ture of  steel. 

The  manganiferous  silver  ore  consists  of  manganese  and  iron 
oxides  bearing  a  sufficient  amount  of  silver  to  pay  for  its  profitable 
extraction.  Gold  is  sometimes  present  in  these  ores  and  not 
infrequently  the  carbonate  of  lead.  The  ores  in  this  class  that  are 
the  richest  in  silver  and  lead  are  used  for  the  extraction  of  these 
two  metals.  The  iron  and  manganese  content  sometimes  assures 
a  higher  price  because  of  their  fluxing  properties.  If  the  silver 
and  lead  content  is  too  low  to  pay  for  the  profitable  extraction  of 
these  metals  but  rich  in  their  iron  and  manganese  content  they 


250  ECONOMIC  GEOLOGY 

are  utilized  directly  in  the  manufacture  of  ferromanganese  and 
spiegeleisen.  If  the  percentage  of  silver,  lead,  manganese  and  iron 
are  too  low  to  pay  for  the  profitable  extraction  of  any  one  of  these 
metals  the  ores  are  sold  directly  as  a  flux  and  the  lead  and  silver 
content  reclaimed  as  a  by-product. 

The  manganese  zinc  residuum  is  derived  from  the  treatment  of 
the  manganiferous  and  zinciferous  ores  of  Franklin  Furnace, 
New  Jersey.  It  consists  largely  of  the  oxides  of  manganese  and 
iron  which  remain  after  the  zinc  has  been  converted  into  its 
oxide,  ZnO.  Zincite,  willemite,  franklinite  and  rhodochrosite 
are  the  common  minerals.  Rhodochrosite  is  also  found  as  a 
gangue  mineral  at  Rico,  Colorado,  and  Butte,  Montana. 

Geographical  Distribution. — Manganese  minerals  exist  in 
all  deep-sea  deposits,  in  many  shallow-water  deposits,  and  in 
terrestrial  deposits.  There  are  four  distinct  belts  of  manganese 
minerals  in  the  United  States:  (1)  The  Appalachian  belt;  (2)  the 
Central  district;  (3)  the  Cordilleran  section;  and  (4)  the  Pacific 
Coast  belt. 

(1)  Appalachian  belt:  This  belt  stretches  in  a  northeasterly 
direction  from  Alabama  on  the  south  to  Nova  Scotia  on  the 
north.  The  ores  result  from  the  decomposition  of  Cambro- 
Ordovician  limestones  and  shales  and  appear  largely  as  nodular 
masses  in  the  residual  clay. 

Two  localities  in  Georgia  are  important.  They  are  Carters- 
ville  and  Cave  Spring.  In  the  former  district  the  ores  are  found 
in  the  residual  clays  derived  from  the  decomposition  of  the 
Beaver  limestone  and  the  Weisner  quartzite,  and  in  the  latter  field 
the  manganese  deposits  occur  only  in  the  clays  that  overlie  the 
Knox  dolomite.  R.  A.  F.  Penrose  attributed  the  source  of  the 
manganese  to  the  underlying  Cambro-Silurian  crystalline  rocks. 
T.  L.  Watson,  however,  considers  that  the  crystalline  terranes  to 
the  east  and  the  south  furnished  the  ores,  for  no  appreciable 
amount  of  manganese  is  found  in  the  parent  rocks  from  which  the 
clays  were  derived.  In  any  event  the  manganese  was  dissolved 
from  the  older  rocks  as  a  carbonate  or  sulphate  and  deposited 
from  circulating  solutions  in  the  residual  clays. 

According  to  H.  Ries  there  are  two  localities  also  for  manganese 
minerals  in  Virginia,  the  James  River  valley  in  the  Piedmont 
region  and  the  Appalachian  area.  In  the  former  field  the  ores 
occur  in  the  residual  clays  and  sands  that  have  been  derived  from 
their  associated  crystalline  terranes.  Nodular  masses  sometimes 


USEFUL  METALS  251 

weighing  500  Ib.  have  been  obtained.  These  nodules  are  scat- 
tered through  a  yellowish-brown  clay  that  form  a  nearly  vertical 
layer  between  a  decomposed  granite  and  the  residual  material 
derived  from  a  quartzose  mica  schist. 

The  more  important  deposits  of  the  Appalachian  Valley  area 
occur  in  a  series  of  irregularly  distributed  materials  along  the 
west  foot  of  the  Blue  Ridge  mountains  for  a  distance  of  about  150 
miles.  The  manganese  ores  occur  in  pockets  in  the  clays  of 
residual  or  sedimentary  character  along  the  contact  of  the  Lower 
Cambrian  quartzites  with  the  overlying  formations. 

There  are  many  scattered  occurrences  of  manganese  ores  along 
the  Appalachian  belt  in  the  more  northern  portion  of  the  area. 
Those  in  the  western  part  of  Vermont  at  Brandon,  are  the  most 
important  and  these  have  from  time  to  time  been  mined.  The 
ore  is  psilomelane.  Both  pyrolusite  and  braunite  are  found  in 
Brandon,  Bennington  and  Plymouth.  Rhodonite  occurs  in 
Topsham,  Vermont,  near  the  village  of  Waits  River  in  masses 
of  sufficient  size  to  be  of  considerable  commercial  value  for  decora- 
tive interior  work,  but  the  value  of  the  material  was  largely 
destroyed  through  prospecting  for  chalcopyrite  in  the  60's. 

(2)  Central  District. — The  most  important  manganese  deposits 
of  the  central  belt  are  found  in  the  neighborhood  of  Batesville, 
Arkansas.     The  ores  are  derived  from  the  decomposition  of  the 
Ordovician,  Silurian,  and  Carboniferous  limestones.     The  lower 
deposits,  perhaps  enriched  by  the  leaching  of  the  Silurian  ores, 
are  the  most  important  because  of  their  higher  manganese  content 
and  their  greater  freedom  from  phosphorus. 

(3)  Cordilleran  Section. — Alabandite  occurs  on  Snake  River, 
Colorado,    along   with   rhodochrosite,    argentite,   and   galenite. 
The  manganese  silver  minerals  occur  at  Leadville,  Colorado. 
In  Utah  the  oxides  of  manganese  occur  in  the  residual  deposits 
from  the  Triassic  limestones. 

(4)  Pacific  Coast  Belt. — Two  localities  in  California  contain 
manganese  deposits.     The  first  of  these  consists  of  pyrolusite 
and  psilomelane  which  occur  in  veins  in  Calaveras  formations 
of  Carboniferous  age  in  Plumas  County  and  elsewhere  in  the 
Sierra  Nevada   Mountains.     The  second   field   lies   along   the 
coast,  both  to  the  north  and  to  the  south  of  San  Francisco.     The 
ores  appear  as  thin  lenses,  interbedded  with  the  jaspers  of  the 
Franciscan  formations  of  Jura-Trias  age.     At  the  Ladd  mine 
the  ore  bodies  are  found  as  cavity  fillings,  infiltrations,  replace- 


252 


ECONOMIC  GEOLOGY 


ment  deposits,  and  as  veins  and  breccia  cement  in  a  fault  fissure 
in  jasper. 


FIG.  125. — The  manganese  deposits  at  Pedras  Pretas,  near  Bahia,  Brazil, 
as  shown  by  shafts  and  pits. 

In  Cuba,  near  Santiago,  pyrolusite,  manganite,  braunite  and 
wad  occur  as  replacement  deposits  with  jaspers.  Perhaps  the 
Brazilian  deposits  are  the  most  noted  ore  bodies  of  manganese  in 


w 


E 


48  km— 


FIG.  126. — Section  across  the  Cretaceous  basin  of  Bahia,  Brazil,  showing 
the  geologic  position  of  manganese  deposits. 

the  world.     (See  Figs.  125  and  126).     The  ore  is  from  25  to  30  ft. 
in  thickness  and  thins  out  toward  the  edges  producing  large  lens- 


USEFUL  METALS 


253 


shaped  masses  that  somewhat  resemble  bedded  deposits.  A  single 
lump  of  ore  weighing  over  3000  Ib.  has  been  obtained.  The  cost 
of  labor  and  railway  transportation  is  $4.95  per  ton.  The  price  of 
the  ore  as  determined  by  the  Illinois  Steel  Company  of  South 


Manganese  beds  indicated  by  thick  black  lint. 

FIG.  127. — Map  showing  the  manganese  bearing  horizons  in  the  Cambrian 
rocks  of  Merionethshire,  North  Wales.     (After  J.  G.  Goodchild.) 

Chicago,  and  the  Carnegie  Steel  Company  of  Bessemer,  Pennsyl- 
vania, ranges  from  $9  to  $  10  per  ton.  Therefore  the  approximate 
profit  is  $5  per  ton.  Fifteen  cents  per  ton  is  deducted  for  each 
per  cent,  of  silica  exceeding  8  per  cent.  The  Brazilian  ore  con- 
tains 1.05  per  cent,  of  silica.  Two  cents  per  unit  is  deducted  for 


254  ECONOMIC  GEOLOGY 

each  0.02  per  cent,  in  excess  of  0.2  per  cent,  of  phosphorus.  The 
Brazilian  ore  carries  only  0.03  per  cent,  of  phosphorus.  The  ore 
dried  at  212°  at  Chicago  allows  12  per  cent,  of  iron  and  remain- 
ing moisture.  The  Brazilian  ore  carries  but  7.6  per  cent,  of  iron 
and  water  combined.  The  tenor  of  manganese  required  is  40 
per  cent.,  while  the  ore  carries  54.8  per  cent,  manganese.  The 
ore,  therefore,  is  destined  to  make  Brazil  one  of  the  principal 
competitors  in  the  world's  markets,  and  to  supply  quite  largely 
the  manganese  ores  for  the  United  States.  The  Michigan  and 
Wisconsin  ores  carry  8  per  cent,  of  manganese.  The  residues 
of  Franklin  Furnace,  New  Jersey,  carry  from  14  to  25  per  cent, 
of  manganese.  The  Vermont  ores  carry  from  30  to  50  per  cent, 
of  manganese.  The  Arkansas  ores  contain  from  40  to  50  per 
cent,  manganese.  Therefore  none  of  the  American  ores  are  so 
rich  in  their  manganese  content  as  the  Brazilian  deposits  of  the 
metal.  These  lower  grade  ores  are  best  adapted  for  the  manu- 
facture of  brick,  glass  and  chemicals. 

India  and  Russia  also  possess  enormous  deposits  of  manganese 
ore. 

Geological  Horizon. — The  ores  of  manganese  are  not  confined 
to  any  particular  geological  horizon.  (See  Fig.  127.)  They 
appear  in  the  Appalachian  belt  in  the  Cambro-Silurian  formations. 
In  Arkaoisas  the  formations  bearing  manganese  range  from  the 
Ordoviciam:  to  the  Carboniferous.  In  the  Harz  Mountains  the 
ores  are  Lower  Permian.  In  California  some  of  the  deposits  are 
as  late  a&  the  Jura-Trias.  In  fact,  bog  manganese  is  in  the  process 
of  formation  to-day  in  the  same  manner  and  through  the  same 
agencies  as  bog  iron  ores. 

Methods  of  Extraction. — Metallic  manganese  may  be  manu- 
factured by  the  action  of  metallic  sodium  upon  the  chlorides  of 
the  metal,  or  by  the  Goldschmidt  process.  In  this  process  the 
ores  of  manganese  are  converted  into  their  oxides  by  roasting. 
The  oxides  are  treated  with  aluminum  at  a  high  temperature 
when  the  oxide  of  aluminum,  AUOs,  is  formed  and  the  manga- 
nese is  reduced  to  the  elemental  state.  The  process  depends 
upon  the  fact  that  aluminum  has  a  greater  affinity  for  oxygen 
than  manganese. 

Uses  of  Manganese. — Before  the  advent  of  the  Christian  era, 
manganese  was  used  to  color  porcelain  violet,  purple,  brown  and 
black.  A  small  amount  of  manganese  imparts  a  violet  color, 
and  an  excess  of  manganese  produces  a  jet  black.  This  black 


USEFUL  METALS  255 

color  is  often  seen  in  door  knobs.  Intermediate  amounts  pro- 
duce the  purple  and  brown  colors.  The  intensity  of  heat  also 
effects  the  color.  The  oxide  acts  as  a  decolorizer  in  ordinary 
glass,  and  therefore  corrects  the  green  color  imparted  by  iron. 

Manganese  ores  are  used  largely  in  the  manufacture  of  chlorine 
for  the  chlorination  of  gold.  In  the  manufacture  of  bromine 
where  the  ore  acts  as  a  carrier  of  oxygen.  Manganese  ores  are 
used  in  the  manufacture  of  oxygen  from  potassium  chlorate 
where  the  black  oxide  of  manganese  plays  the  part  of  a  catalytic 
agent.  Manganese  ores  are  also  used  in  the  manufacture  of 
disinfectants.  Here  it  serves  as  an  oxidizing  agent.  They  are 
also  used  as  a  gas  purifier  in  the  place  of  bog  iron.  Manganese 
ores  are  quite  largely  used  in  the  disposal  of  municipal  sewage, 
for  manganese  ore  becomes  an  important  oxidizer  with  the  appli- 
cation of  heat. 

They  are  also  used  in  the  manufacture  of  potassium  permanga- 
nate and  the  various  salts  of  the  metal  for  the  chemical  trade. 
They  are  also  used  as  a  flux  in  silver-lead  smelting,  and  in  voltaic 
batteries  as  a  strong  negative  electrode.  Manganese  ores  are 
used  as  a  drier  in  varnishes,  as  a  coloring  agent  in  calico  printing, 
in  the  manufacture  of  pottery,  brick  and  many  paints. 

Nine-tenths  of  all  metallic  manganese  is  used  in  the  manufac- 
ture of  steel  and  in  the  alloys  of  the  metal.  In  the  manufacture 
of  steel  two  manganese  alloys  are  employed.  The  one  is  spiegel- 
eisen,  with  less  than  25  per  cent,  of  manganese  and  with  a 
general  average  of  20  per  cent,  manganese.  The  other  is  ferro- 
manganese,  with  more  than  25  per  cent,  of  manganese  and  a 
general  average  of  80  per  cent,  manganese.  The  general  ratio  of 
spiegeleisen  to  ferromanganese  is  1:4.  The  effect  produced 
upon  steel  is  intricate  and  very  important.  (1)  It  prevents  the 
formation  of  gas  cavities  during  the  solidification  of  the  steel. 
(2)  It  restores  the  necessary  carbon  to  the  steel.  (3)  It  re- 
moves oxygen  from  the  iron  in  the  steel  and  (4)  it  imparts  great 
hardness  and  toughness  to  the  steel.  A  superior  quality  of 
toughness  is  imparted  by  less  than  3  per  cent,  of  manganese. 
With  from  3  to  20  per  cent  of  manganese  the  steel  is  particu- 
larly well  adapted  for  many  purposes  where  great  abrasion  is 
encountered,  as  in  mine  car  wheels;  in  milling  and  crushing  ma- 
chinery; in  coupling-pins;  in  car  rails  for  curves,  switches,  freight 
yards  and  wherever  heavy  traffic  is  common. 

One  of  the  newest  uses  for  manganese  lies  in  the  manufacture 


256  ECONOMIC  GEOLOGY 

of  safes,  where  the  results  are  extremely  satisfactory.  The  body 
of  the  safe  is  cast  in  one  solid  piece.  The  door  which  is  also  of 
manganese  steel  is  grooved  and  fitted  into  the  doorway  so  accu- 
rately that  the  joint  is  perfectly  tight  and  explosive  liquids  are 
not  successfully  forced  into  the  safe.  The  ordinary  files  and 
chisels  are  useless  in  finishing  the  safe,  therefore  air-driven  abra- 
sive wheels  are  employed.  The  groove  fits  so  perfectly  that  all 
attempts  to  open  the  safe  by  burglars'  tools  and  high-grade  ex- 
plosives have  thus  far  failed. 

In  a  classification  of  the  uses  by  means  of  the  purity  of  the  ores 
the  following  division  may  be  made.  (1)  The  very  low-grade 
ores  are  used  in  the  chemical  trade,  in  the  manufacture  of  glass, 
brick  and  pottery.  (2)  The  high-grade  ores  are  used  in  the 
manufacture  of  spiegeleisen  and  ferromanganese. 

Manganese  is  also  used  in  the  manufacture  of  manganese 
bronze,  which  consists  of  manganese  and  copper  with  or  without 
iron.  It  is  furthermore  utilized  in  silver  bronze,  which  consists 
of  manganese  and  copper,  together  with  silver,  aluminum  and 
zinc.  It  is  also  used  in  the  manufacture  of  titanium  alloys. 
Many  of  the  complex  alloys  of  which  manganese  steel  is  a  con- 
stituent are  capable  of  wide  industrial  application. 

In  spite  of  the  numerous  uses  of  manganese  ores,  and  the  wide 
application  of  manganese  steel,  the  production  of  manganese  in 
the  United  States  is  comparatively  small.  The  most  important 
eastern  locality  is  Virginia.  Most  of  the  manganese  for  domestic 
consumption  is  imported  from  Brazil.  Cuba  entered  the  race 
for  the  first  time  in  1900.  It  is  therefore  to  be  expected  that 
Cuba  will  continue  to  be  an  important  contributor  of  high-grade 
manganese  ores  for  the  market  of  the  United  States. 

Zinc ;  Its  Properties,  Occurrence  and  Uses 

Properties. — Zinc,  symbol  Zn,  is  a  bluish-white  crystalline 
metal.  At  a  temperature  of  100°  it  becomes  soft,  and  at  150° 
it  is  ductile  and  malleable.  It  can  therefore  be  readily  rolled 
into  sheets  or  drawn  into  wire.  The  sheets  and  wires  do  not 
become  brittle  again  upon  returning  to  the  normal  temperature. 
At  a  temperature  of  300°  C.,  zinc  can  be  rendered  pulverulent. 
The  metal  tarnishes  readily  in  moist  atmosphere,  becoming 
coated  with  a  basic  carbonate  of  the  metal.  In  dry  atmosphere 
at  the  ordinary  temperature  it  remains  permanent.  Ordinary 


USEFUL  METALS  257 

commercial  zinc  is  readily  soluble  in  the  mineral  acids.  It  burns 
in  an  atmosphere  of  oxygen  with  a  bluish  flame  to  zinc  oxide. 
Its  specific  gravity  is  7.1;  melting  point  419°  C.,  boiling  point, 
918°,  and  its  atomic  weight  is  65.37. 

Ores  of  the  Metal. — Native  Zinc,  Zn,  100  per  cent.  Zn.  This 
metal  has  been  reported  from  eastern  Alabama  and  from  near 
Melbourne,  Australia,  but  the  occurrences  are  not  completely 
authenticated. 

Sphalerite,  ZnS,  67  per  cent.  Zn.  Often  with  resinous  luster. 
(Isometric). 

Wurtzite,  ZnS,  67  per  cent.  Zn.  Many  massive  blendes  are 
mixtures  of  these  two  minerals.  (Hexagonal.) 

Smithsonite,  ZnCOs,  51.96  per  cent.  Zn.  When  earthy  and 
impure  it  is  called  dry  bone  by  American  miners. 

Hydrozincite,  2ZnCO3,Zn(OH)2;  60  per  cent.  Zn. 

Zincite,  ZnO,  80.3  per  cent.  Zn.     Deep  red  to  orange  yellow. 

Franklinite,  (Fe,Mn,Zn)0,(Fe,Mn)203.  A  spinel  of  variable 
composition. 

Voltzite,  4ZnS,ZnO.     A  rather  rare  oxysulphide  of  zinc. 

Goslarite,  ZnSO4,7H20,  28.2  per  cent.  ZnO. 

Calamine,  ZnSiOs,Zn(OH)2,  54.2  per  cent.  Zn. 

Willemite,  Zn2Si04,  58.5  per  cent.  Zn. 

Origin  of  the  Ores. — Zinc  is  fairly  common  but  not  widely 
diffused  in  nature.  Dieulaf ait  reports  its  occurrence  in  sea  water. 
It  has  also  been  found  in  the  ashes  of  sea  weeds.  The  occurrence 
of  native  zinc  in  northeastern  Alabama,  in  Shasta  County, 
California,  and  near  Melbourne,  Australia,  need  confirmation. 
If  native  zinc  occurs  in  these  localities  it  is  probably  a  reduction 
product. 

The  sulphide  of  zinc  is  by  far  the  most  important  source  of  the 
metal.  It  is  known  as  sphalerite,  blende,  or  black-jack  when 
crystallized  in  the  isometric  system,  and  as  wurtzite  when  in 
the  hexagonal  system.  The  massive  blendes  are  mechanical 
mixtures  of  these  two  minerals.  The  sulphide  of  zinc  is  precipi- 
tated in  the  laboratory  by  the  action  of  ammonium  sulphide 
upon  the  soluble  salts  of  zinc,  or  by  the  action  of  hydrogen  sul- 
phide upon  an  alkaline  solution  of  the  metal.  According  to 
H.  de  Senermont,  sphalerite  is  formed  when  zinc  solutions  are 
heated  in  a  sealed  tube  in  an  atmosphere  of  hydrogen  sulphide. 
According  to  F.  W.  Clarke,  sphalerite  is  formed  in  nature  at 
relatively  low  temperatures  and  at  the  higher  temperatures  it  is 

M 


258  ECONOMIC  GEOLOGY 

transformed  into  wurtzite.  An  ore  body,  therefore,  containing 
wurtzite  is  probably  a  product  of  high  temperatures.  What 
these  temperatures  are  and  at  what  temperature  the  transforma- 
tion of  sphalerite  to  wurtzite  takes  place  remain  to  be  determined. 
Sphalerite  has  been  produced  by  the  action  of  decaying  wood 
upon  the  solutions  of  zinc  sulphate  in  old  zinc  mines.  According 
to  H.  A.  Wheeler,  the  massive  blendes  occur  at  North  St.  Louis, 
Missouri,  embedded  in  lignite,  where  these  blendes  have  evidently 
been  formed  by  the  action  of  organic  matter  upon  soluble  zinc 
compounds.  C.  R.  Keyes  reports  sphalerite  crystals  on  iron 
nails  that  have  been  immersed  in  mine  waters  for  15  years. 
W.  P.  Jenney  cites  the  occurrence  of  sphalerite  upon  the  walls  of 
a  tunnel  that  has  been  closed  and  filled  with  mine  waters  for 
several  years.  Crystals  of  sphalerite  have  also  been  observed 
upon  the  pick  marks  in  abandoned  zinc  mines.  Sphalerite  in 
its  association  with  the  lead  mines  of  the  Mississippi  Valley 
appears  to  be  of  secondary  origin. 

According  to  J.  D.  Robertson,  zinc  sulphide  occurs  at  Galena, 
Kansas,  as  a  white  mud  mingled  with  acid  water.  Evidently 
the  zinc  was  brought  into  solution  by  the  oxidation  of  sphalerite 
and  thrown  out  of  solution  either  by  the  action  of  sulphureted 
waters  or  by  organic  matter. 

Smithsonite  is  a  secondary  mineral  of  metasomatic  origin. 
Wherever  zinciferous  solutions  percolate  through  limestones  a 
reaction  follows  with  the  deposition  of  the  zinc  as  smithsonite 
in  the  place  of  the  removed  calcium  compounds.  G.  Bischoff 
reports  several  instances  in  which  smithsonite  has  formed  as  a 
deposit  from  natural  waters.  The  alteration  of  the  zinc  ores  in 
Missouri  and  Arkansas  has  given  rise  to  a  zinciferous  clay  known 
as  tallow  clay. 

Zincite  and  franklinite  at  Franklin  Furnace,  New  Jersey,  form 
a  unique  deposit  produced  by  contact  metamorphism.  This 
ore  deposit  will  be  discussed  in  detail  a  little  later  in  this  chapter. 

Goslarite  is  an  oxygenated  secondary  mineral.  It  occurs  as  a 
solid  in  the  Rammelsberg  mine  near  Goslar  in  the  Harz  Moun- 
tains, at  Schemnitz  in  Hungary,  and  elsewhere.  It  is  formed 
through  the  oxidation  of  sphalerite.  It  is  present  in  solution  in 
mine  waters  and  zinciferous  mineral  springs.  It  is  in  this  form 
that  zinc  is  leached  out  of  zinciferous  rocks  and  transported 
elsewhere  for  subsequent  deposition  as  an  ore  body. 

Willemite,  which  has  come  into  prominence  through  the  study 


USEFUL  METALS  259 

of  the  emanations  of  radium,  is  often  a  product  of  contact 
metamorphism. 

Character  of  the  Ore  Bodies. — Zinc  ores  occur  in  nature  under 
a  great  variety  of  conditions,  which  may  be  classified  as  follows : 
(1)  As  true  metalliferous  veins.  (2)  As  cavity  fillings  not  of 
true-fissure  vein  type.  (3)  As  irregular  masses  in  the  metamor- 
phic  rocks.  (4)  As  irregular  masses,  or  disseminations,  formed 
by  replacement  or  impregnation  in  limestones  and  quartzites. 
(5)  As  contact  metamorphic  deposits.  (6)  In  residual  clays. 

The  associated  minerals  are  galenite,  pyrite,  marcasite,  and, 
less  frequently,  chalcopyrite,  together  with  calcite,  dolomite, 
fluorite  and  barite  as  gangue  minerals.  In  the  zone  of  weathering 
in  zinciferous  ore  bodies  the  sulphides  are  altered  to  smithsonite, 
hydrozincite  or  calamine.  The  oxidized  ore  often  yields  more 
readily  to  metallurgical  treatment  than  the  sulphide  ores,  and 
even  though  the  percentage  of  zinc  may  be  lower  they  may  be 
of  greater  value  than  the  unoxidized  ores. 

Where  zinc  and  lead  occur  together  as  sulphides  the  zinc  dis- 
integrates more  rapidly  than  the  lead  and  its  sulphate  solutions 
are  transferred  downward  for  the  enrichment  of  the  ore  bodies  at 
the  lower  levels. 

Geographical  Distribution. — The  zinc  ores  of  the  United  States 
are  located  in  three  distinct  belts  as  follows:  (1)  The  Appalachian 
belt;  (2)  the  Central  belt,  and  (3)  the  Cordilleran  section. 

(1)  Appalachian  Belt. — There  are  several  scattered  occurrences 
of  zinc  ores  in  this  belt.  Some  of  these  produce  small  quantities 
of  lead,  as  in  Tennessee  and  southwestern  Virginia.  The  ores 
are  associated  with  the  Cambro-Ordovician  limestones.  The 
unoxidized  ores  consist  of  sphalerite,  galenite,  pyrite,  and  belong  to 
the  disseminated  replacement-breccia,  type.  The  oxidized  ores, 
which  are  concentrated  in  the  residual  clays  in  close  proximity  to 
the  weathered  surface  of  the  limestones,  consist  of  smithsonite, 
cerussite  and  calamine. 

In  Pennsylvania,  in  the  Saucon  Valley,  an  ore  body  of  zinc 
occurs  that  at  one  time  bid  fair  to  be  of  considerable  commercial 
significance  but  the  ore  body  has  never  been  extensively  worked. 
In  Thetford,  Vermont,  sphalerite  and  galenite  occur  in  a  fissure 
vein  with  a  quartz  gangue  in  the  Vershire  schists. 

The  most  important  ore  body  of  zinc  in  this  belt  occurs  at 
Franklin  Furnace,  N.  J.  According  to  A.  C.  Spencer,  two  large 
bodies  of  zinciferous  ore,  different  in  character  from  any  other 


260  ECONOMIC  GEOLOGY 

known  ore  deposit,  occur  at  Mine  Hill,  near  Franklin  Furnace, 
and  at  Sterling  Hill,  near  Ogdensburg.  The  ores  consist  of  vary- 
ing proportions  of  franklinite,  zincite  and  willemite  admixed  with 
calcite,  and  in  some  instances  with  the  silicates  rhodonite,  garnet 
and  tephroite.  In  some  parts  of  the  vein  franklinite  is  the  only 
important  mineral  present.  In  some  instances  it  is  accompanied 
by  willemite;  in  others  only  by  zincite,  and  some  cases  by  both 
minerals.  Occasionally  the  ore  consists  of  zincite  set  in  a  matrix 
of  coarsely  crystallized  calcite. 

At  Mine  Hill  the  zinc  content  ranges  from  23  to  29  per  cent. 
The  iron  ranges  from  19  to  22.5  per  cent.  The  manganese  from 
6  to  12  per  cent.  The  zinc  content  of  the  Sterling  Hill  ore  is 
somewhat  less  than  the  per  cent,  given  above.  The  ore  at  Mine 
Hill  comprises  a  layer  varying  in  thickness  from  12  to  100  ft. 
or  even  more,  bent  upon  itself  to  form  a  long  trough  with  sides  of 
unequal  height.  The  outcrop  of  the  ore  is  about  2,600  ft.  in 
length. 

A.  C.  Spencer  regards  the  Sterling  Hill  deposits  also  as  com- 
prising a  trough.  The  layer  ranges  in  thickness  from  10  to  30 
ft.  In  some  parts  of  the  layer  the  ore  consists  largely  of  frank- 
linite and  in  others  of  zincite.  The  sides  of  the  trough  are  of 
unequal  height  and  strike  in  a  northeasterly  direction.  The  dip 
of  the  veins  range  from  45  to  60  degrees. 

According  to  A.  C.  Spencer,  the  deposits  must  have  been  intro- 
duced either  before  or  during  the  metamorphism  of  the  containing 
limestones  and  the  igneous  rocks  which  are  now  gneisses.  He 
regards  the  main  ore  body  at  both  Sterling  Hill  and  Mine  Hill 
as  injected  bodily  into  the  limestones  like  igneous  intrusions, 
and  the  leaner  ores  of  Sterling  Hill  as  deposited  by  magmatic 
waters  which  permeated  and  replaced  the  associated  limestones. 
According  to  J.  F.  Kemp,  the  ore  was  deposited  from  solutions 
stimulated  by  granitic  intrusions  subsequently  metamorphosed 
into  gneisses.  According  to  J.  E.  Wolff,  the  ores  are  contempora- 
neous in  form  and  structure  with  the  enclosing  limestones,  and 
therefore  older  than  the  granites. 

(2)  Central  States. — In  the  Central  belt  the  Joplin  district  is  the 
most  important  producer  of  zinc.  In  fact  it  is  one  of  the  most 
important  zinc-mining  camps  of  the  world.  The  geological  sec- 
tion consists  of  Mississippian  cherts  and  limestones  overlaid  with 
Pennsylvanian  limestones,  shales,  sandstones,  with  occasional 
beds  of  coal.  All  these  terranes  are  of  Carboniferous  age. 


USEFUL  METALS 


261 


According  to  E.  T.  Hancock,  the  ore  deposits  fall  into  two 
groups :  First,  runs  and  their  modifications ;  and  second,  blanket 
veins,  or  sheet  ground  deposits.  The  runs  are  irregular,  usually 
elongated,  sometimes  tabular  and  inclined  bodies  of  ore  uniformly 
associated  with  disturbed  strata  which  are  brecciated,  slicken- 
sided  and  faulted.  The  runs  are  generally  a  few  hundred  feet 


FIG.  128. — Depression  in  the  limestone  extending  down  to  the  Grand 
Falls  chert  member,  filled  with  Cherokee  shale,  Joplin,  Missouri,  (After 
W.  S.  Tangier-Smith  and  C.  E.  Siebenthal,  U.  S.  Geological  Survey.) 

in  length  but  the  Arkansas  run  exceeds  1000  ft.  The  runs  also 
have  an  average  width  of  about  50  ft.  and  a  maximum  width  of 
300  ft.  The  roughly  elliptical  closed  runs  constitute  one  of  the 
most  distinctive  and  constantly  recurring  types  of  ore  bodies  in 
the  Joplin  District. 

The  blanket  veins  are  nearly  horizontal,  tabular  ore  bodies 
extending  parallel  with  the  bedding  planes  of  the  limestones  and 


FIG.  129. — Depression  in  the  limestone  extending  down  to  the  Grand 
Falls  chert  member,  filled  with  shale  and  compressed.  Joplin,  Missouri. 
(After  U.  S.  Tangier-Smith  and  C.  E.  Siebenthal,  U.  S.  Geological  Survey.) 

cherts.     The  typical  sheet  ground  appears  to  be  developed  inva- 
riably in  the  Grand  Falls  chert. 

In  the  vertical  distribution  of  the  ores  the  sulphide  of  lead  is  the 
most  abundant  in  the  upper  portions  of  the  ore  deposits  and  the 
sulphide  of  zinc  in  the  lower  portions.  This  distinction,  however, 
is  not  universal.  The  most  profitable  mining  is  confined  to  the 


262 


ECONOMIC  GEOLOGY 


Boone  limestones  that  overlie  the  base  of  the  Grand  Falls  chert 
(Figs.  128  and  129). 

Concerning  the  genesis  of  the  ore  bodies,  W.  S.  Tangier-Smith 
says: 


FORMATION 


CHARACTER   OF    ROCKS 


Cherokee 


-UNCONFORMITY 


Carterville 

— UNCONFORMITY 

(  Short  Creek 
oolite  member,) 


Boone 


(Grand  Falls 
chert  member.) 


150+ 


120) 


Drab  to  black  shale  and  gray  to 
buff  sandstone  with  occasional 
beds  of  coal. 


Light  to  dark  shales  and  shaly 
and  oolitic  limestone  with 
same  massive  soft  to  hard 
sandstones, 


Massive  homogeneous  bed  or 
oolitic  limestone. 


Limestone,  in  large  part  crystal- 
line, with  interbedded  chert. 


Heavy  -bedded,  solid  chert. 


FIG.  130. — Generalized  geologic  section  of  the  Joplin,  Missouri  district. 
(By  permission  of  the  Macmillan  Company,  from  Ries'  Economic  Geology.) 


"The  common  association  of  the  lead  and  zinc  ores  with  the  lime- 
stones, the  known  occurrence  of  these  metals  in  sea  water,  their  probable 
precipitation  in  minute  quantities  in  limestones  laid  down  in  these  waters; 
the  actual  wide-spread  occurrence  of  lead  and  zinc  in  very  small  amount 
in  the  limestones  of  the  Mississippi  Valley,  both  Carboniferous  and 
Cambro-Ordovician,  together  with  the  general  course  of  circulation 


USEFUL  METALS 


263 


reaching  the  Joplin  district  is  through  the  lead  and  zinc-bearing  calcar- 
eous formations,  render  it  reasonably  certain  that  these  formations  are 
the  source  of  the  ore  bodies." 

The  immediate  source  of  the  ores  is  the  various  limestones 
situated  below  the  Pennsylvanian  terranes. 

The  method  of  mining  at  Joplin  is  peculiar  to  that  district 
alone.  The  land  holder  leases  the  property  for  ten  years  for  a 
royalty  of  8  per  cent,  to  15  per  cent,  of  the  gross  value  of  the  out- 
put. The  leasee  prospects  by  drilling  and  sinking  shafts,  by 


FIG.  131. — View  near  Linden  in  Wisconsin  lead  and  zinc  district.     (By 
permission  of  the  Macmillan  Company,  from  Ries'  Economic  Geology.} 

cross  cutting  and  drifting,  and  then  subleases  for  a  royalty  of 
from  15  per  cent,  to  25  per  cent,  of  the  gross  output  of  the  ores. 
Three  results  are  said  to  have  followed  this  method.  1 .  The  dis- 
covery of  many  new  ore  bodies.  2.  Freedom  from  serious  labor 
troubles.  3.  Increase  in  the  annual  output  of  zinc,  so  that  the 
Joplin  district  has  become  the  premier  area  of  the  world  (Fig.  130) . 
Other  important  districts  are  located  in  Wisconsin,  Arkansas, 
Kentucky  and  Illinois.  (See  Fig.  131.) 

3.  Cordilleran  Region. — In  the  Cordilleran  district  the  best  rep- 


264  ECONOMIC  GEOLOGY 

resentative  is  found  in  Colorado.  This  belt  possesses  argentif- 
erous zinc  sulphide  with  sufficient  lead  and  iron  to  render  the 
ore  undesirable  for  the  manufacture  of  zinc.  In  1899  Wales  and 
Belgium  entered  the  market  and  bought  largely  of  the  Colorado 
ores.  Favorable  freight  rates  were  obtained  by  way  of  Galveston, 
Texas,  to  Swansea  and  Antwerp,  viz.,  $10  per  ton.  The  value 
placed  at  the  mine  was  $3  per  ton.  Although  the  commodity 
purchased  by  Wales  and  Belgium  was  a  zinc  concentrate,  it  was 
removed  as  a  by-product  which  enhanced  the  value  of  the  remain- 
der of  the  products,  thereby  leading  to  a  more  profitable  develop- 
ment of  the  zinc  resources  of  the  state.  There  is  now  in  operation 
a  zinc  smelter  at  Pueblo,  Colorado,  and  a  zinc  oxide  plant  at 
Canyon  City,  Colorado. 

In  Cumberland  and  Derbyshire,  England,  sphalerite  with  some 
smithsonite  occurs  in  the  Carboniferous  limestones.  Here,  as  at 
Joplin,  Missouri,  the  sulphide  of  zinc  is  far  more  abundant  in  the 
lower  portions  of  the  ore  body  than  the  sulphide  of  lead.  In 
both  localities  smithsonite  is  fairly  abundant  and  occurs  as  a  true 
metasomatic  deposit  due  to  the  reaction  of  zinciferous  solutions 
upon  the  associated  limestones.  On  the  island  of  Sardinia,  meta- 
somatic zinc  ores  occur  at  the  junction  of  limestones  with  non- 
calcareous  beds,  which  contact  may  represent  either  a  fault  line 
or  a  plane  of  normal  sedimentation.  Many  of  the  Sardinia 
deposits  below  the  zdne  of  weathering  carry  the  characteristic 
zinc  sulphides  as  their  permanent  ore.  The  Grecian  ore  to  the 
southwest  of  Athens  consists  largely  of  the  sulphides  of  lead  and 
zinc,  associated  with  siderite.  Thomas  and  MacAlister  consider 
the  zinciferous  solution  of  hydro  thermal  origin.  As  they  came  up 
from  below  they  passed  through  small  fissures  in  the  associated 
shales  without  depositing  their  metallic  content.  The  presence  of 
the  calcareous  material  caused  a  deposition  of  the  ores  at  the  junc- 
tion of  the  limestones  with  interbedded  shales. 

In  Upper  Silesia  the  ores  of  zinc  occur  in  Triassic  limestone  and 
dolomite  interbedded  with  mottled  sandstones.  In  the  Picos  de 
Europa  district  in  the  Province  of  Asturias,  Spain,  the  zinciferous 
ores  are  associated  with  limestones  of  Carboniferous  age,  and  of 
Cretaceous  age  in  the  Santander  district. 

Geological  Horizon. — The  ores  of  zinc  do  not  seem  to  be  con- 
fined to  any  particular  geological  horizon.  Those  of  the  Appala- 
chian belt  as  already  noted  are  Cambro-Ordovician.  On  the 
island  of  Sardinia  they  belong  to  the  same  age.  At  Joplin, 


USEFUL  METALS  265 

Missouri,  and  Cumberland,  England,  they  are  Carboniferous. 
The  Westphalian  ores  lie  often  in  the  Devonian  limestones,  while 
in  the  Alpine  district,  in  Carinthia,  the  zinciferous  ores  are  most 
abundant  in  the  Triassic  limestones. 

Methods  of  Extraction. — (1)  The  Calcination  Process. — The 
sulphide  ore  is  first  calcined  to  liberate  the  sulphur  and  convert 
the  metal  into  its  oxide  according  to  the  following  equation: 
ZnS+3O  =  ZnO+SO2.  If  the  ore  is  the  carbonate  it  is  also  cal- 
cined to  drive  off  the  carbonic  acid  present  according  to  the  equa- 
tion, ZnC03  =  ZnO+C02.  If  the  ore  is  the  oxide  it  may  also 
be  calcined  to  drive  off  any  sulphur  that  may  be  present  or  liber- 
ate any  other  volatile  constitutents.  The  oxide  obtained  by 
calcination  is  dissolved  in  dilute  mineral  acid,  precipitated  as  a 


FIG.  132. — Zinc  mine  and  mill  of  the  Northern  Ore  Company,   Edwards, 

New  York. 


carbonate,  and  converted  into  its  oxide,  which  is  finally  reduced  to 
the  elemental  state  with  charcoal  obtained  from  sugar  (Fig.  132). 

(2)  The  Electrolytic  Process. — According  to  Ashcroft  and  Swin- 
burne, good  results  are  obtained  by  this  process  and  a  large  inter- 
est is  attached  to  the  method  which  is  especially  applicable  to  the 
sulphides  of  zinc. 

(3)  Fusing   with    Calcium    Carbide. — In   some   localities   the 
sulphides  of  zinc  are  fused  with  calcium  carbide  and  from  the 
resulting  product  several  useful  metals,  as  copper,  etc.,  are  easily 
obtained. 

(4)  Distillation. — At  lola,  Kansas,  a  considerable  amount  of 
zinciferous  ores  have  been  treated  with  natural  gas  as  a  fuel. 
The  standard  furnace  distills  25,000  Ib.  of  ore  with  45  per  cent,  of 


266  ECONOMIC  GEOLOGY 

coke  or  poor  coal  as  a  reducing  agent.     Unfortunately  the  supply 
of  natural  gas  at  lola  is  becoming  exhausted. 

Uses  of  Zinc. — Zinc  enters  the  marts  of  trade  in  the  form  of 
rolled  sheets,  and  also  in  cast  cakes  1  in.  in  thickness.  In 
the  latter  form  it  is  known  as  spelter.  Spelter  cakes  are  extremely 
brittle  and  break  with  a  crystalline  fracture.  If  the  metal  is 
pure,  the  crystal  faces  are  large  and  present  a  smooth  or  perfect 
cleavage.  If  small  quantities  of  iron  are  present,  dull  spots 
appear  on  the  crystal  face,  and  with  only  a  small  percentage  of 
iron  present,  the  spelter  breaks  with  granular  fracture.  Spelter  is 
seldom,  if  ever,  pure.  Particular  notice  should  be  given  to  iron 
in  spelter.  The  iron  does  not  distill  with  the  zinc.  It  comes  from 
the  apparatus  used  in  the  distillation,  and  the  stirring  rods  util- 
lized  in  the  process  of  cooling. 

Zinc  is  intimately  associated  with  both  the  iron  and  the  copper 
industries.  Galvanized  iron  is  used  in  wire  nettings,  corrugated 
roofing,  water  tanks,  etc.  Galvanized  iron  is  not  produced  by 
electrolytic  deposition  as  the  name  implies,  but  by  dipping  the 
iron  in  a  bath  of 'molten  zinc.  The  coating  of  zinc  preserves  the 
iron  from  rusting.  It  is  far  better  able  to  withstand  the  corrosive 
action  of  moist  air  and  water  than  ordinary  tinned  iron.  The 
film  of  zinc  is  heavier  than  the  corresponding  film  of  tin,  therefore 
the  protuberances  of  the  sheet  iron  are  more  perfectly  protected. 

Zinc  is  used  in  a  large  number  of  useful  alloys,  especially  with 
copper.  English  brass  consists  of  1  part  of  zinc  and  2  parts 
of  copper.  Dutch  brass,  consists  of  10  parts  of  zinc  and  5  parts 
of  copper.  Muntz  metal  of  1  part  of  zinc  and  3  parts  of  copper. 
Some  varieties  of  bronze,  1  part  of  zinc,  4  parts  of  tin,  and  95  parts 
of  copper. 

With  copper,  tin,  and  antimony,  zinc  will  mix  in  all  proportions. 
With  lead  and  bismuth  the  alloys  of  zinc  are  of  definite  propor- 
tions. The  presence  of  zinc  increases  both  the  hardness  and  the 
durability  of  the  alloy. 

Zinc  is  used  in  the  desilverization  of  lead,  also  as  a  precipitant 
for  gold  from  potassium  cyanide  solutions.  The  form  used  may 
be  sheet  zinc,  zinc  scraps,  granulated  zinc,  or  zinc  dust.  The 
last  form  is  more  widely  used  than  any  of  the  others  because  it 
presents  a  larger  surface  to  the  action  of  the  cyanide  solutions. 
Three  grains  of  gold  per  ton  of  solution  may  yield  a  profit. 
One-half  pound  of  zinc  will  completely  reduce  to  the  elemental 
state  all  the  gold  in  a  ton  of  these  dilute  solutions. 


USEFUL  METALS  267 

Zinc  is  used  in  the  manufacture  of  zinc  oxide,  or  zinc  white, 
which  is  now  extensively  used  as  a  pigment  in  the  place  of  white 
lead.  It  is  manufactured  by  burning  metallic  zinc  in  an  atmos- 
phere of  oxygen  or  in  a  current  of  air.  It  does  not  equal  white 
lead  in  covering  power  or  body,  but  it  is  vastly  superior  to  white 
lead  wherever  the  walls  of  the  building  are  exposed  to  the  action 
of  hydrogen  sulphide,  as  in  chemical  or  mineralogical  labora- 
tories, and  in  cities  and  towns  where  large  quantities  of  coal  are 
consumed. 

Zinc  is  used  also  in  the  manufacture  of  zinc  salts  for  the 
chemical  trade.  Perhaps  the  most  important  salt  of  zinc  is  the 
chloride.  It  is  used  to  a  limited  extent  in  dentistry  for  spongy 
gums.  It  is  utilized  extensively  in  preserving  railroad  ties. 
The  tie  is  immersed  in  a  solution  of  zinc  chloride,  and  after 
becoming  thoroughly  saturated,  the  life  of  the  tie  is  much 
prolonged.  This  new  use  is  increasing  rapidly  with  many  of 
the  larger  railroads. 

Zinc  is  used  also  in  electrolysis  and  in  the  manufacture  of 
white  vitriol.  It  is  used  in  the  manufacture  of  lithopone,  a 
pigment  consisting  of  barite,  zinc  oxide,  and  zinc  sulphate. 
The  industry  is  carried  on  to  a  considerable  extent  by  the  New 
Jersey  Zinc  Company  and  by  the  Grasselli  Chemical  Company. 
White  vitriol  is  largely  consumed  in  the  manufacture  of  glue  and 
special  paints. 

The  most  important  commercial  and  technical  change  in  the 
zinc  industry  in  recent  years  appears  in  the  predominance  which 
the  natural  gas  smelters  of  Kansas  have  gained  over  those  depend- 
ing upon  coal  for  a  fuel.  The  Joplin  ores  were  formally  treated 
at  LaSalle  and  Peru,  Illinois,  St.  Louis,  Missouri,  and  Pittsburg, 
Kansas.  The  first  two  were  smelting  centers  long  before  the 
history  of  zinc  began  at  Joplin.  The  last  is.  only  26  miles  from 
Joplin  and  owes  its  development  to  the  local  coal  production. 
The  use  of  natural  gas  has  resulted  in  closing  down  the  coal 
smelters  and  the  installation  of  gas  smelters. 


CHAPTER  IX 
THE  RARE  METALS 

MOLYBDENUN,  TUNGSTEN,  TITANIUM,  ZIRCONIUM,  VANADIUM, 

URANIUM,    COLUMBIUM,     TANTALIUM, 

SELENIUM,  TELLURIUM 

Molybdenum 

Properties. — Molybdenum,  symbol  Mo,  is  one  of  the  rarer 
metals.  Its  specific  gravity  is  8.6,  and  its  atomic  weight  96. 

Mode  of  Occurrence. — Molybdenum  is  a  member  of  the  same 
elementary  group  with  chromium,  but  its  geological  affinities  are 
widely  different.  It  occurs  as  a  primary  constituent  of  the  acid 
rocks,  like  granite,  rather  than  the  basic  rocks  like  peridotite, 
the  home  of  chromite.  The  metal  does  not  occur  free  in  nature 
and  is  not  widely  diffused. 

Ores  of  Molybdenum. — The  sulphide  of  the  metal,  molyb- 
denite, MoS2,  is  the  most  important  ore.  This  mineral  closely 
resembles  graphite,  but  may  be  easily  distinguished  from  it. 
Graphite  is  quickly  copper-plated  when  in  contact  with  a  strip 
of  zinc  in  a  solution  of  CuS04;  molybdenite  is  slowly  copper- 
plated  under  the  same  conditions.  Graphite  is  unaffected  by 
HNOs;  but  molybdenite  is  oxidized  to  MoOs.  The  molybdates  of 
several  metals  are  well  known  as  natural  minerals:  Wulfenite, 
PbMoO4;  powellite,  CaMo04;  pateraite,  CoMoO4;  belonesite, 
MgMoO4;  and  molybdic  ocher,  Fe2(Mo04)3,7iH2O.  The  oxide 
of  molybdenum  occurs  as  a  secondary  mineral,  molybdite,  MoO3. 

Origin  of  Ores. — Molybdenite,  the  most  important  source  of 
the  metal,  is  of  primary  origin.  According  to  G.  O.  Smith,  it 
occurs  at  Cooper,  Maine,  as  an  impregnation  deposit.  It  occurs 
in  the  pegmatite  dikes  and  their  associated  granites.  The  oxides 
and  ocher  are  always  of  secondary  origin. 

Character  of  Ore  Bodies. — A.  R.  Crook  has  observed  large 
masses  of  molybdenite  in  quartz  veins  in  granite  at  Crown  Point, 
Washington.  The  author  has  observed  molybdenite  on  the  east- 
ern coast  of  Newfoundland  in  large  quartz  veins  traversing 
sandstones  and  conglomerates.  In  Maine  it  occurs  in  pegmatite 

268 


THE  RARE  METALS  269 

dikes  and  the  adjacent  granites.  In  Canada  it  is  often  associated 
with  granites,  and  also  appears  in  veins  cutting  limestone. 
J.  W.  Wells  has  observed  molybdenite  in  pyroxenite,  as  though 
produced  by  contact  metamorphism. 

Geographical  Distribution. — Molybdenum  ores  are  found  in 
small  quantities  in  the  northern  Appalachian  belt;  in  the  Cordil- 
leras, especially  in  Utah;  in  the  Pacific  Coast  belt,  in  California 
and  Washington;  in  Canada  and  Newfoundland. 

Geological  Horizon. — The  ores  seem  to  be  more  abundant  in 
the  pre-Cambrian,  Cambrian  and  Ordovician  terranes,  but  the 
Devonian  granites  sometimes  carry  molybdenite. 

Method  of  Reduction. — Molybdenum  may  be  reduced  to  the 
elemental  state  by  the  action  of  nascent  hydrogen  upon  the 
oxide  or  chloride. 

Uses. — Molybdenum  is  used  in  the  manufacture  of  several 
important  alloys,  and  in  tool  steel.  It  renders  steel  hard  and 
tough.  It  is  used  in  the  manufacture  of  chemical  salts,  the  most 
important  of  which  is  ammonium  molybdate,  used  largely  to 
determine  the  presence  of  phosphorus  in  iron  ores  and  in  steel. 
Molybdenum  is  used  as  a  fire-proofing  material,  as  a  germicide, 
and  as  a  disinfectant.  Sodium  molybdate  is  used  to  color 
pottery  and  porcelain  blue,  and  to  dye  silks  and  woolens.  Molyb- 
denum tannate  is  used  to  color  leather,  and  molybdenum  indigo 
to  color  india-rubber. 

The  production  of  molybdenum  in  the  United  States  is  small. 
Ordinary  years  furnish  about  50  tons  of  molybdenite,  containing 
92  per  cent,  of  the  sulphide,  MoS2. 

Tungsten 

Properties. — Tungsten,  symbol  W,  is  one  of  the  acid-forming 
heavy  metals.  It  is  closely  allied  with  molybdenum,  and  is  in 
the  same  elementary  group  with  chromium.  Its  melting  point 
is  1700°  C.;  its  specific  gravity  is  19.1,  and  its  atomic  weight  is 
184. 

Ores  of  Tungsten. — The  ores  of  tungsten  are  not  numerous. 
They  are  mostly  tungstates  of  the  metals.  The  tungstate  of 
calcium,  scheelite,  and  tungstite,  the  oxide,  are  important. 

Wolframite,  (Fe,Mn)WO4,  is  the  most  important  among  the 
tungstates  of  the  metals;  Hubnerite,  MnW(>4,  is  a  tungstate  of 
manganese;  reinite,  FeWO^  stolzite,  PbWO^  cuprotungstite,  Cu- 
WO4;  scheelite,  CaW04,  and  tungstite,  WO3. 


270  ECONOMIC  GEOLOGY 

Origin  of  the  Ores. — Wolframite  is  both  a  primary  and  a 
secondary  mineral.  In  the  Cornish  tin  mines,  wolframite  is  a 
companion  of  cassiterite,  the  most  important  ore  of  tin.  The. 
two  minerals  may  appear  as  primary  segregations.  While 
tungsten  is  an  annoying  impurity,  a  by-product  is  obtained 
which  is  used  in  the  manufacture  of  the  sodium  tungstate  of 
commerce.  According  to  J.  D.  Irving,  wolframite  occurs  with 
cassiterite  in  the  Etta  tin  district  of  the  Black  Hills,  South 
Dakota.  Primary  wolframite  has  been  observed  in  quartz 
veins  cutting  granite;  and  secondary  wolframite  in  associated 
limestones,  apparently  formed  by  metasomatic  replacement. 
At  Oscola,  Nevada,  the  tungstate  of  manganese  is  abundant  in 
veins  of  quartz  cutting  a  porphyritic  granite.  Scheelite,  the 
tungstate  of  calcium,  is  also  present  in  the  same  veins.  Htib- 
nerite  occurs  with  scheelite  and  wolframite  in  similar  veins  in  the 
Dragoon  Mountains,  Arizona.  At  Trumbull,  Conn.,  the  ores 
are  wolframite,  scheelite  and  tungstite.  At  Longhill,  Conn., 
scheelite  occurs  along  the  contact  of  limestones  with  hornblende 
gneiss  and  diorite.  Scheelite  occurs  in  the  Province  of  Quebec 
in  quartz  veins  cutting  slates  and  sandstones.  Its  association 
is  with  the  acid  intrusives,  as  granites  and  pegmatites,  rather  than 
the  ultra-basic  rocks,  as  peridotite. 

Character  of  the  Ore  Bodies. — Tungsten  minerals  occur  as 
masses  (lens-shaped)  in  the  early  segregation  of  an  acid  magma; 
in  veins  cutting  acid  intrusives;  in  limestones,  by  metasomatic 
replacement;  and  as  contact  deposits  between  limestones  and 
their  intrusives. 

Geographical  Distribution. — There  are  three  belts  of  tungsten 
minerals  in  the  United  States:  the  New  England,  the  Cordilleran, 
and  the  Western  belt. 

Geological  Horizon. — The  ores  seem  to  be  confined  to  the  acid 
intrusives  of  the  older  geological  formations. 

Method  of  Extraction. — The  metal  is  most  easily  extracted 
from  scheelite,  the  tungstate  of  calcium. 

Uses. — The  largest  and  the  most  important  use  of  tungsten 
is  in  the  manufacture  of  tool  steel.  It  imparts  both  hardness 
and  toughness  to  the  steel.  It  is  this  use  which  renders  the 
mining  of  tungsten  minerals  profitable.  According  to  F.  L.  Hess : 

"  The  introduction  of  tungsten  into  steel  gives  it  the  property  of  holding 
a  temper  at  a  much  higher  temperature  than  high-carbon  steels.  When 
lathe  tools  are  made  from  tungsten  steel,  the  lathes  may  be  speeded  up 
until  the  chips  leaving  the  tool  are  so  hot  that  they  turn  blue." 


THE  RARE  METALS  271 

The  percentage  of  tungsten  in  tool  steel  varies  with  the  manu- 
facturers. Some  use  from  1J  to  3J  per  cent.;  others  from  16  to 
20  per  cent,  of  tungsten.  According  to  C.  A.  Edwards,  the  hard- 
est steel  recorded  contained  19.37  per  cent,  tungsten.  Tungsten 
is  added  to  steel  in  the  form  of  an  alloy  of  tungsten  and  iron 
carrying  from  40  to  82  per  cent,  of  the  former  metal.  Alloys 
of  tungsten  with  copper  and  aluminum  are  well  known,  and  of 
considerable  technical  value.  A  small  quantity  of  tungsten 
added  to  aluminum  greatly  improves  its  resistance  to  erosion, 
and  increases  its  tensile  strength.  Tungsten  is  used  in  the 
manufacture  of  crucibles  for  electric  furnaces.  Powdered  tung- 
sten is  mixed  with  carbonaceous  matter  in  the  form  of  a  paste, 
pressed  into  the  desired  shape,  and  sintered.  Tungsten  is  used 
as  a  filament  in  incandescent  electric  lamps.  The  extreme 
whiteness  of  the  light  renders  it  far  superior  to  that  of  the  carbon 
incandescent  lamp,  which  it  is  rapidly  supplanting.  It  is  far 
more  efficient  than  the  tantalum  lamp.  The  drawback  is  the 
brittleness  of  the  filament,  and  much  material  is  lost  in  shipment. 
The  advantages  are  its  whiterlight,  its  longer  life,  and  its  use  in 
either  alternating  or  direct  currents.  Metallic  tungsten  has  been 
used  in  arc-lamp  electrodes.  Tungsten  is  used  in  rendering 
curtains,  draperies  and  papers  fire-proof.  It  is  used  as  a  mordant 
in  dyeing,  also  in  weighting  delicate  fabrics.  As  sodium  tung- 
state  has  approximately  the  same  ratio  of  expansion  for  moderate 
temperatures  as  platinum,  it  is  used  for  sealing  platinum  appa- 
ratus for  making  water  determinations  in  rock  analysis.  Tung- 
sten is  used  as  a  pigment  in  the  manufacture  of  glass,  also  of  gold 
and  violet  bronze  powders.  Calcium  tungstate  is  used  as  a 
screen  to  make  X-rays  visible. 

Economics. — The  production  of  tungsten  is  so  closely  related 
to  that  of  pig  iron,  from  which  tungsten  steel  is  manufactured, 
that  the  output  for  1908  was  far  below  that  of  1907.  The  value 
of  its  production  is  as  follows:  1905,  $268,676;  1906,  $348,867; 
1907,  $890,048;  1908,  $229,995;  1909,  $559,900;  1910,  $844,526, 
and  1911,  $407,985;  1912;  $492,000. 

Titanium 

Properties. — Titanium,  symbol  Ti,  is  a  rare  metal,  extremely 
difficult  to  isolate  in  a  pure  state,  owing  to  the  fact  that  it  unites 
directly  with  nitrogen,  forming  a  nitride.  Its  melting  point  is 


272 


ECONOMIC  GEOLOGY 


3,000°  C.;  its  specific  gravity  is  3.543,  and  its  atomic  weight  is 
48.1. 

Mode  of  Occurrence. — Titanium  is  often  catalogued  as  one 
of  the  rarer  elements;  yet  it  is  almost  invariably  present  in  the 
igneous  rocks,  and  in  the  sedimentaries  derived  from  them. 
According  to  F.  W.  Clarke,  out  of  800  igneous  rocks  analyzed 
in  the  laboratory  of  the  U.  S.  Geological  Survey,  784  contained 
titanium.  It  is  found  in  nature  only  in  the  oxidized  state  (Fig. 
133). 


Olir/ne-hyperite 


Hornblende  Rock. 


Mica, 


FIG.  133. — Titaniferous  apatite  vein  in  gabbro.     (After  J.  H.  L.   Vogt.) 


Ores  of  Titanium. — Ilmenite,  FeO,  TiO2,  is  a  faintly  magnetic 
iron-black  mineral,  with  a  black  or  brownish-red  streak.  Several 
varieties  have  been  recognized,  based  on  the  relation  of  the  iron 
to  the  titanium.  The  true  ilmenite  carries  from  26  to  30  per  cent, 
of  titanium.  Menaccanite  carries  from  20  to  25  per  cent,  of 
titanium. 

Leucoxane  is  a  metamorphic  decomposition-product  of  ilmenite 
and  its  numerous  varieties.  It  occurs  as  a  white  or  reddish 
mineral  surrounding  ilmenite. 

Rutile,  Ti02,  shades  in  color  from  reddish-brown  to  black. 
It  occurs  in  tetragonal  crystals,  often  twinned. 


THE  RARE  METALS  273 

Nigrine,  TiO2,  is  a  black  variety,  containing  from  2  to  3  per 
cent,  of  Fe203. 

Ilmenorutile  is  a  black  variety  from  the  Ilmen  Mountains, 
containing  10  per  cent,  or  more  of  Fe203.  It  carries  too 
much  iron  to  be  classified  as  rutile,  and  too  much  titanium  for 
ilmenite. 

Octahedrite,  TiO2,  occurs  in  definite  octahedrons  of  the  tetrag- 
onal system. 

Brookite,  TiO2,  crystallizes  in  the  orthorhombic  system. 

Perovskite,  CaO,TiO2,  is  a  calcium  titanate. 

Titanite,  CaO,TiO2,Si02,  often  called  sphene,  on  account  of  its 
wedge-shaped  crystals. 

The  oxide,  Ti20s,  has  not  been  observed  as  an  independent 
mineral. 

Origin  of  the  Ores. — Ilmenite  is  widely  diffused  throughout 
both  the  acid  and  the  basic  intrusives,  and  on  account  of  its 
basicity  is  one  of  the  earliest  minerals  to  segregate  from  a  cooling 
magma.  Leucoxane  is  always  secondary  in  origin.  Rutile  is  a 
common  constituent  of  the  acid  intrusives,  and  is  occasionally 
found  in  limestones,  dolomites  and  slates.  The  variety  octahe- 
drite  is  always  of  secondary  origin.  Perovskite  is  associated  with 
both  eruptive  and  metamorphic  rocks.  Titanite  is  a  pyrogenic 
mineral  in  the  older  secretions  of  the  acid  intrusives,  as  granites, 
syenites,  etc. 

Character  of  the  Ore  Bodies. — The  titaniferous  iron  ores  occur 
in  considerable  quantities  in  the  State  of  New  York.  They  are 
mined  chiefly  for  their  iron  content,  and  occur  in  more  or  less 
lens-shaped  masses.  Titaniferous  magnetite  is  a  common  mineral 
in  New  York  and  New  England.  In  Nelson  County,  Va.,  large 
dikes  of  pegmatite,  sometimes  hundreds  of  feet  thick,  cut  a 
biotite  gneiss.  Rutile  and  ilmenite  occur  in  these  dikes,  asso- 
ciated with  the  potassium  and  sodium  feldspars,  amphibole, 
hornblende,  quartz  and  apatite.  In  the  pegmatite  itself,  the 
titanium  ores  are  not  sufficiently  abundant  to  become  a  commer- 
cial consideration;  but  the  pegmatites  are  cut  by  veins  or  dikes  of 
rutile,  ilmenorutile,  and  apatite,  which  F.  L.  Hess  considers  as  a 
later  phase  of  the  pegmatites.  At  Roseland,  Virginia,  in  the  same 
county,  the  rutile  comprises  about  4  per  cent,  of  the  pegmatite. 
The  rock  is  crushed  and  concentrated  together  with  the  decompo- 
sition-products that  overlie  the  pegmatite,  to  a  product  containing 
approximately  98  per  cent.  Ti02. 

18 


274  ECONOMIC  GEOLOGY 

Geographical  Distribution. — There  are  three  belts  of  titanium- 
bearing  rocks  in  the  United  States:  (1)  The  Appalachain  belt. 
The  -maximum  development  occurs,  as  above  noted,  in  Nelson 
Co.,  Virginia.  In  Chester,  Pa.,  rutile  occurs  in  exceptionally 
pure  crystals,  which  have  brought  high  prices  for  the  dental  trade 
and  for  museum  specimens.  It  occurs  in  New  York,  where  large 
quantities  of  titaniferous  iron  abound,  and  in  Vermont,  where 
many  fine  crystals  of  rutile  have  been  obtained.  (2)  The  North- 
ern Belt,  where  titaniferous  ores  have  been  mined  in  Minnesota 
in  considerable  quantity.  (3)  In  Wyoming,  where  the  ore  is 
similar  to  that  found  in  Minnesota. 

In  foreign  countries  rutile  is  found  in  Norway,  South  Australia, 
and  Queensland. 

Geological  Horizon. — Titanium  minerals  are  more  abundant 
with  the  pre-Cambrian,  Cambrian,  and  Ordovician  terranes  than 
with  the  later  geological  formations. 

Uses. — The  most  important  use  of  titanium  is  in  the  manufac- 
ture of  steel  and  cast-iron,  to  which  it  imparts  hardness  and 
toughness.  The  alloy  ferro-titanium,  containing  10  to  20  per 
cent,  of  titanium,  is  first  manufactured.  This  is  added  to  the 
molten  iron  so  as  to  produce  a  steel  bearing  0.1  per  cent,  titanium. 
Steel  rails  thus  formed  resist  the  wear  of  heavy  traffic  much  longer 
than  ordinary  rails.  Titanium-thermit  is  another  form  in  which 
titanium  is  introduced  into  steel.  Cupro-titanium  is  an  alloy  of 
titanium  used  in  the  manufacture  of  bronze  and  other  castings 
containing  copper.  Titanium  is  used  in  the  manufacture  of 
electrodes  for  arc-lights.  The  chloride  of  titanium,  TiCl2,  is 
used  in  dyeing.  The  sulphate,  ^(SOJs,  is  used  both  as  a 
striper  and  a  mordant.  The  titanous  potassium  oxalate  is  used 
as  a  yellow  dye  and  a  mordant  in  the  treatment  of  leather. 
Ti(S04)2  is  used  in  ihe  detection  of  fluorine.  The  tile  industry 
also  utilizes  rutile.  It  gives  a  soft,  beautiful  yellow  color  in  tile 
and  brick.  Rutile  is  also  used  to  give  to  artificial  teeth  an  ivory 
tint.  The  nitride  of  titanium  is  sometimes  formed  in  smelting 
titaniferous  iron  ores.  This  compound  has  commercial  possi- 
bilities as  a  fertilizer.  Rutile  finds  some  use  as  a  gem. 

ZIRCONIUM 

Properties. — Zirconium,  symbol  Zr,  is  a  rare  element  closely 
allied  to  titanium.  Its  melting  point  is  1500°  C ;  its  specific  grav- 
ity is  4.15,  and  its  atomic  weight  is  90.6. 


THE  RARE  METALS  275 

Ores  of  the  Metal. — Zircon,  ZrSiO-i,  is  the  most  important 
source  of  the  element  and  its  compounds.  Unlike  the  other  rare 
minerals  to  which  it  is  allied,  it  occurs  chiefly  as  a  silicate  widely 
diffused  in  the  igneous  rocks.  It  is  easily  distinguished  from  all 
other  minerals  by  its  crystal  form;  viz.,  that  of  a  tetragonal 
prism  terminated  by  a  tetragonal  pyramid  at  either  extremity; 
by  its  color,  which  shades  through  brown  and  yellow  to  green; 
and  by  its  hardness  of  7.5. 

Zircon  is  one  of  the  least  alterable  of  all  minerals,  for  it  contains 
no  protoxides,  and  only  the  most  insoluble  of  dioxides.  It,  how- 
ever, passes  into  the  hydrous  state,  producing  amorphous  and  iso- 
tropic  species  or  varieties.  This  is  effected  by  the  loss  of  silica, 
and  the  addition  of  iron  oxides  through  infiltrating  waters.  Auer- 
bachite,  calyptolite,  cryptolite,  malacon,  oerstedite,  and  tachy- 
aphaltite  are  all  altered  varieties  of  zircon. 

In  some  instances,  zircon  seems  to  have  been  of  pneumatolytic 
origin.  According  to  F.  W.  Clarke,  it  is  one  of  the  earliest 
minerals  to  crystallize  from  a  cooling  magma,  and  the  first  of  all 
silicates  to  thus  solidify.  The  varieties  of  zircon  mentioned 
above  are  all  of  secondary  origin,  arising  through  the  hydration 
and  metamorphism  of  zircon. 

Beccarite  is  an  olive-green  variety  of  zircon  from  Ceylon. 

Braddeleyite,  Zr02,  is  an  oxide  of  zircon  found  in  Brazil  and 
Ceylon. 

Geographical  Distribution. — Zircon  is  one  of  the  commonest 
constituents  of  all  classes  of  igneous  rocks.  It  is  more  abundant, 
however,  in  the  acid  than  in  the  basic  intrusives.  It  is  especially 
abundant  in  the  granites,  pegmatites,  syenites,  gneisses,  diorites 
and  pyroxenites,  and  in  the  younger  eruptives.  The  most 
noted  American  locality  is  in  Burke,  McDowell,  Henderson, 
Polk  and  Rutherford  Counties,  N.  C.,  where  it  occurs  in  the  gold- 
bearing  monazite  sands,  due  to  the  disintegration  of  granite  and 
gneissoid  rocks.  At  Grenville,  Canada,  it  occurs  in  a  crystalline 
limestone,  in  association  with  wollastonite,  titanite  and  graphite. 

Geological  Horizon. — Zircon  is  not  restricted  to  any  horizon, 
for  it  occurs  in  the  igneous  rocks  of  all  ages. 

Method  of  Extraction. — Zircon  is  separated  from  its  matrix  by 
rough  crushing  and  washing.  A  clean  separation  can  be  made 
with  electrical  machinery  and  by  careful  washing.  A  small 
quantity  of  zircon  is  obtained  as  a  by-product  from  the  monazite 
concentrates. 


276  ECONOMIC  GEOLOGY 

Uses. — The  metal  is  obtained  in  two  forms,  one  amorphous, 
the  other  crystalline.  The  former  burns  readily  in  the  air,  the 
latter  only  at  the  high  temperature  of  the  oxyhydrogen  flame. 
The  oxide,  ZrO2,  is  the  most  important  salt.  It  is  reported  to 
have  been  used  in  the  tile  and  pottery  industries.  The  demand 
for  zircon  is  small.  It  has  been  supplied  in  the  United  States 
by  the  intermittent  working  of  the  mines  near  Zirconia,  N.  C. 
The  crystals  of  Zircon  are  larger  in  Henderson  County,  where  they 
occur  in  pegmatites,  than  elsewhere  when  associated  with 
monazite.  The  crystals  of  zircon  are  larger  also  in  the  peg- 
matites than  they  are  in  the  granitic,  gneissoid,  or  hornblendic 
rocks. 

Only  a  few  hundred  pounds  of  zircon  are  obtained  during  an 
entire  year,  and  in  some  years  there  seems  to  be  no  recorded 
output  of  the  mineral. 

Vanadium 

Properties. — Vanadium,  symbol  V,  is  a  rare  element  closely 
allied  to  phosphorus.  It  acts  both  as  an  acid  and  a  base. 
The  metal  is  permanent  at  ordinary  temperatures,  but  is  rapidly 
oxidized  to  V2O5  when  heated.  Its  melting  point  is  1680°  C.; 
its  specific  gravity  is  5.5,  and  its  atomic  weight  is  51.2. 

Ores  of  Vanadium. — Vanadinite,  3PbO,  V2O5,  PbCl2,  is  the 
most  common  vanadium  mineral. 

Desdoizite,  4RO,  V2O5,  H20.     (R  =  Pb,  Zn,  in  ratio  1  :  1.) 

Cuprodescloizite,  4RO,  V205,  H2O.     (R  =  Pb,  Zn,  Cu.) 

Pucherite,  Bi20s,  V20s,  is  a  vanadate  of  bismuth. 

Mottramite  is  a  vanadate  of  lead  and  copper. 

Carnotite  is  a  vanadate  of  uranium  and  potassium  of  some 
commercial  significance  where  it  occurs  as  canary  yellow  impreg- 
nations in  the  sandstones  of  western  Colorado  and  eastern  Utah. 

Roscoelite  is  a  vanadium  silicate  of  the  mica  family,  where 
vanadium  occurs  displacing  aluminum.  The  color  ranges  from 
a  clove-brown  to  a  dark  greenish-brown. 

There  are  many  rare  minerals  bearing  small  percentages  of 
vanadium.  These  are  most  common  in  the  ferromagnesian 
rocks.  They  are  present  in  the  titaniferous  magnetites,  and  in 
rocks  of  nearly  every  class,  whether  of  igneous  or  of  sedimentary 
origin.  Vanadium  has  been  observed  in  bauxite,  cryolite, 
rutile,  peat,  lignite,  and  in  the  ashes  of  wood. 


THE  RARE  METALS  277 

Origin  of  Ores. — Small  quantities  of  primary  vanadium  may 
occur  in  the  segregation  of  titaniferous  magnetites.  Carnotite 
occurs  as  impregnation  deposits  in  sandstones.  It  occurs  also 
in  the  pegmatite  veins  of  Radium  Hill,  South  Australia.  Where 
carnotite  occurs  on  or  near  partially  altered  vegetable  matter, 
organic  substances  have  acted  as  precipitants  for  vanadium. 
Mottramite  occurs  as  an  impregnation  deposit  in  England, 
where  it  has  attained  some  commercial  significance.  Roscoelite 
is  found  sparingly  in  the  gold  veins  of  Boulder  County,  Colorado, 
and  in  Granite  Creek,  California,  several  pounds  of  roscoelite 
were  wasted  in  the  extraction  of  the  included  gold. 

Geographical  Distribution. — Workable  deposits  are  chiefly 
confined  to  the  Cordilleran  belt.  Colorado  and  Utah  are  the 
most  promising;  but  vanadinite  ores  have  been  produced  com- 
mercially in  Arizona  and  New  Mexico. 

Geological  Horizon. — Small  quantities  of  vanadium  may  be 
found  in  the  rocks  of  all  ages;  but  the  workable  deposits  of 
western  Colorado  and  eastern  Utah  are  in  Jurassic  and  Cretaceous 
sandstones. 

Uses. — Like  titanium,  vanadium  finds  its  most  important  use 
in  the  manufacture  of  steel.  Even  small  quantities  of  the 
metal  impart  a  remarkable  toughness  to  the  steel.  In  the  manu- 
facture of  steel  it  removes  both  oxygen  and  nitrogen,  and  forms 
carbides,  with  beneficent  effect  upon  the  finished  product. 
Vanadium  steel  resists  both  shock  and  fatigue  far  better  than 
ordinary  steel.  It  is  therefore  well  fitted  for  saws,  springs,  and 
mechanical  tools  in  general.  Vanadium  is  introduced  into  steel 
either  as  an  alloy  with  chromium,  or  with  manganese,  or  both. 
To  these  alloys  nickel  is  sometimes  added.  Each  metal  present 
tends  to  make  the  resulting  steel  both  hard  and  tough.  Vanadi- 
um is  also  used  in  the  manufacture  of  cast  iron,  brass  and  bronze. 

When  3  to  5  parts  per  1,000  are  added  to  steel,  vanadium 
communicates  remarkable  properties.  It  doubles  the  coefficient 
of  resistance  to  fracture  under  all  circumstances  (as  shock,  crush- 
ing, elongation,  etc),  and  at  the  same  time  imparts  such  extreme 
hardness  as  to  make  it  possible  to  reduce  the  armor  of  vessels  in 
thickness  almost  one-half.  The  reason  that  the  effect  of  0.5  or 
0.3  per  cent,  of  vanadium  is  so  general  and  intense  on  steel  lies  in 
the  extreme  avidity  vanadium  has  for  oxygen.  The  presence  of 
minute  traces  of  the  metal  in  a  bath  of  molten  steel  would  lead  to 
an  immediate  and  absolute  reduction  of  every  trace  of  iron  oxide. 


278  ECONOMIC  GEOLOGY 

Now,  the  rupture  of  the  best  prepared  steel  is  due  to  traces  of  the 
oxides  of  Fe, — even  microlites  of  Fe2O3  act  like  the  stroke  of  a 
diamond  on  the  thickest  glass.  Vanadium  steel  acquires  its 
maximum  hardness  not  by  tempering,  but  by  annealing  at  700° 
to  800°  C.  A  planing  machine  with  vanadium  steel  cutting  edges 
can  be  set  at  work  with  the  greatest  velocity,  and  even  when 
heated  at  red-heat,  it  still  continues  to  take  off  shavings  of  iron 
or  casting  without  exhibiting  any  signs  of  exhaustion.  This 
property  is  of  vital  importance  in  projectiles.  The  shock  they 
receive  upon  striking  their  mark  raises  them  to  a  very  high  tem- 
perature, yet  vanadium  steel  retains  all  its  sharpness,  and  its  pene- 
trating force  remains  intact.  Ordinary  steel  softens  and  loses  its 
cutting  power.  Vanadium  is  destined  to  cause  a  revolution  in 
armaments. 

The  salts  of  vanadium  have  considerable  commercial  signifi- 
cance. F.  L.  Hess  states  that  metavanadic  acid  is  used  as  a 
substitute  for  gold  bronze  in  paint;  that  vanadium  chloride  is 
used  as  a  mordant  in  printing  fabrics;  that  vanadium  trioxide 
is  used  as  a  mordant  in  dyeing;  and  that  vanadium  pentoxide  is 
used  as  a  reducing  agent  in  the  treatment  of  organic  compounds 
in  an  acid  bath.  This  anhydride  is  also  used  in  the  place  of 
platinum  in  the  contact  process  for  the  manufacture  of  H2SO4, 
and  as  a  photographic  developer.  Vanadin  is  a  medicinal  prep- 
aration with  potassium  chlorate.  Vanadium  salts  are  also  used 
as  fertilizers,  in  coloring  glass,  and  in  the  manufacture  of  a  water- 
proof black  ink. 

Economics. — The  price  paid  for  vanadic  acid  in  1910  was 
about  $2.50  per  pound  according  to  purity.  The  price  paid  for 
the  alloy  ferro-vanadium  was  about  $5  per  pound  of  vanadium 
content. 

UEANIUM 

Properties. — Uranium,  symbol  U,  is  a  rare  and  heavy  metal. 
Its  melting  point  is  800°  C;  its  specific  gravity  is  18.7,  and  its 
atomic  weight  is  238.5 — the  highest  of  all  known  elements. 

Ores  of  the  Metal.— Uraninite,  xU02,  yU03,  with  some  PbO, 
and  a  little  N.  It  crystallizes  in  isometric  octahedrons,  but  usu- 
ally occurs  massive  and  granular.  The  color  varies  in  shades  of 
gray,  green  and  black.  In  uraninite,  helium  was  first  discovered 
and  later  polonium.  Both  uranium  and  its  compounds  are 


THE  RARE  METALS  279 

radioactive,  and  uranium  itself  may  be  the  progenitor  of  its  more 
highly  active  companion,  radium.  The  mineral  is  remarkable 
in  that  it  presents  the  only  instance  in  which  nitrogen  has  been 
found  belonging  to  the  original  crust  of  the  earth.  Uranniobite 
is  the  crystallized  variety  of  uraninite  in  which  the  element  nitro- 
gen occurs  in  its  maximum  percentage,  2.6  per  cent. 

Broggerite,  U02,  U03,  Th02,  occurs  in  octahedral  crystals. 

Cleveite,  U02,U03,ThO2,  Y203,  the  trioxide,  UO3,  is  present  in 
larger  percentage  in  cleveite  than  in  the  preceding  minerals. 
It  crystallizes  in  hexahedrons,  often  modified  by  other  funda- 
mental isometric  forms. 

Nivenite,  U02,  U03,  Th02,  Y203,  occurs  massive,  velvet-black  in 
color  and  is  more  soluble  than  the  other  varieties  of  uraninite. 

Pitchblende,  U02,  U03,  is  massive  uraninite.  Th02  and  the 
rare  earths  are  absent,  while  nitrogen  is  sparingly  present,  if 
represented  at  all. 

Coracite  is  an  alteration  product  of  uraninite  in  its  transition  to 
gummite. 

Gummite,  (PbCa)U3,  SiOi2,  6H20,  is  an  alteration  product  of 
uraninite  which  occurs  in  rounded  or  flattened  pieces,  closely 
resembling  gum. 

Carnotite  is  cited  by  H.  Ries  as  occurring  in  Montrose  County, 
Colo.,  and  also  in  Utah.  Carnotite  is  a  vanadate  of  uranium  and 
potassium  which  occurs  in  canary-yellow  impregnations  in  sand- 
stones in  western  Colorado  and  eastern  Utah.  It  is  second  in 
importance  of  the  uranium-bearing  minerals. 

There  are  several  well  known  hydrous  arsenates  and  phosphates 
of  uranium  and  the  alkaline  earth  metals,  but  they  are  not  of 
commercial  significance. 

Origin  of  the  Ores. — Most  of  the  minerals  bearing  uranium  are 
of  secondary  origin.  The  columbates  and  tantalates  of  iron 
containing  uranium  are  primary  constituents  of  pegmatites. 

Character  of  Ore  Bodies. — Uraninite  is  sometimes  obtained 
from  metalliferous  veins,  but  more  often  it  is  found  in  association 
with  acid  intrusives,  granites  and  pegmatites.  In  Colorado  it  is 
obtained  from  a  schistose  granite  which  in  places  gives  way  to 
porphyry.  Uranium  is  chemically  unlike  vanadium,  with  which 
it  is  associated  in  one  of  its  most  important  ores;  viz.,  carnotite. 
Uranium  has  been  found  in  coal;  in  an  anthracitic  mineral  in  a 
pegmatite  vein  in  Canada;  in  anthracitic -bitumen  from  Sweden; 
and  in  the  ashes  of  seaweeds.  Carnotite  occurs  as  impregnation 


280  ECONOMIC  GEOLOGY 

deposits  in  sandstones.  It  occupies  the  interstices  between  the 
grains,  and  occurs  in  thin  coatings  in  the  cracks  and  crevices  of 
the  rocks.  In  some  instances,  lumps  of  several  inches  in  thick- 
ness have  been  obtained.  These  lumps  are  very  pure. 

Geographical  Distribution. — Uraninite  and  gamotite  occur  in 
Montrose  County,  Colorado,  and  also  in  Utah.  Pitchblende  is 
found  in  Gilpin  County,  Colo.  Carnotite  occurs  in  Montrose, 
San  Miguel,  Dolores,  Rio  Blanco,  and  Routt  Counties,  Colo., 
and  in  the  eastern  part  of  Utah. 

Geological  Horizon. — In  southwestern  Colorado,  the  carnotite 
deposits  are  in  Jurassic  sandstones,  and  in  northwestern  Colorado 
in  Cretaceous  sandstones. 

Extraction  of  the  Metal. — Uranium  salts  have  been  extracted 
at  the  Haynes  plant  near  Cedar,  Colo.;  but  the  haul  both  for  ore 
and  supplies  is  long  and  expensive.  The  ore  is  of  low  grade,  and 
the  problem  of  commercial  extraction  is  difficult. 

Uses. — Uranium,  unlike  the  other  rare  metals  considered  above 
in  this  chapter,  does  not  find  its  most  important  use  in  the  manu- 
facture of  steel.  This  use  will  be  considered  later. 

Uranium  minerals  and  their  salts  are  radioactive.  They  have 
given  rise  to  the  study  of  radiology,  and  to  a  new  method  for  the 
determination  of  the  age  of  the  earth  through  radium  emana- 
tions. A  careful  study  of  the  data  published  along  this  line 
places  the  age  of  the  earth  at  approximately  100,000,000  years. 
A  pocket-knife,  keys,  coins,  or  any  piece  of  metal  may  be  covered 
with  uraninite  and  placed  on  a  photographic  plate  in  a  dark 
room;  and  in  a  few  days,  upon  the  development  of  the  plate, 
photographs  of  the  objects  will  be  obtained. 

Uranium  hardens  and  toughens  steel,  like  its  associate,  vana- 
dium. It  is  used  in  Germany  in  the  manufacture  of  steel  and 
ferro-alloys,  and  of  gun-barrels. 

The  salts  of  uranium  are  used  in  the  manufacture  of  pottery 
glazes  and  iridescent  glass.  The  double  acetate  of  uranium  and 
sodium  is  used  in  the  determination  of  phosphates.  Uranyl 
acetate  is  used  in  medicine  as  a  precipitant  for  proteids,  and  in  the 
chemical  laboratory  in  the  volumetric  determination  of  zinc.  In 
this  determination,  the  nitrate  may  be  substituted  for  the  acetate. 
The  nitrate  is  also  used  in  the  manufacture  of  glazes;  in  photog- 
raphy; in  the  chemical  laboratory  in  the  determination  of  arsenic 
and  phosphoric  acid,  and  in  the  detection  of  morphine.  The 


THE  RARE  METALS  281 

trioxide  is  used  to  paint  porcelain  red,  and  is  also  used  in  calico 
printing. 

Columbium 

Properties. — Columbium,  symbol  Cb,  is  a  rare  acid-forming 
element,  closely  allied  to  tantalum.  Its  melting  point  is  1950°  C, 
its  specific  gravity  is  7.2,  and  its  atomic  weight  is  93.5. 

Ores  of  the  Metal. — Columbite,  FeO,  Cb2O5,  is  a  columbate  of 
iron.  It  crystallizes  in  the  orthorhombic  system.  Its  color  is 
brownish-black  to  black. 

Manganocolumbite,  MnO,  Cb205,  is  a  columbate  of  manganese, 
in  which  manganese  has  displaced  the  iron  of  normal  columbite. 
Iron  may  be  present  in  considerable  quantity. 

Samarskite,  R"2,  R'"3,  (CbTa)602i,  where  R"  =  Fe,  Ca,  U02 
and  R'"  =  Ce,Y.  The  mineral  is  a  rare  columbate  and  tantalate 
of  iron,  calcium,  uranium,  and  the  rare  earth  metals. 

Euxenite  is  a  columbate  and  titanate  of  the  rare  earths.  It  is  an 
altered  samarskite. 

Pyrochlore  is  a  metacolumbate  of  calcium  and  cerium. 

Fergusonite  is  a  metacolumbate  of  Y,  Er,  Ce  and  U. 

Sipylite  is  a  columbate  of  erbium. 

There  are  several  other  rare  minerals  of  which  columbium  is  a 
constituent. 

Character  of  the  Ore  Bodies.— Columbite  is  a  primary  mineral, 
found  in  the  acid  intrusives,  granites  and  pegmatites.  In  these 
veins  single  masses  of  columbite  have  been  obtained  weighing 
more  than  2000  pounds. 

Geographical  Distribution. — Columbite  is  found  sparingly  in 
the  Appalachian  belt  in  North  Carolina,  Virginia,  Pennsylvania, 
New  York,  New  Hampshire,  Connecticut  and  Maine.  In  Maine, 
columbite  is  associated  with  cassiterite.  In  New  Hampshire, 
at  Acworth,  it  is  associated  with  beryl;  in  New  York,  at  Green- 
field, it  is  associated  with  c'hrysoberyl.  The  Appalachian  belt  is 
scarcely  of  commercial  significance.  Columbite  occurs  in  Colo- 
rado near  Canon  City,  and  at  the  Etta  mine  in  the  Black  Hills, 
South  Dakota.  The  largest  masses  found  in  America  occurred  in 
the  Etta  mine  in  association  with  cassiterite. 

Uses. — The  interest  attached  to  columbium  at  present  is  due 
to  the  incandescent  lamp  industry.  There  is  little  if  any  pro- 
duction of  columbite  other  than  for  the  tantalum  present,  and 
for  museum  and  laboratory  materials. 


282  ECONOMIC  GEOLOGY 

TANTALUM 

Properties. — Tantalum,  symbol  Ta,  is  an  acid-forming  element 
closely  allied  to  columbium,  with  which  it  is  generally  associated. 
It  is  ductile,  malleable,  sectile,  hard,  tough,  and  readily  with- 
stands corrosion.  Its  melting  point  is  2250°  C.,  its  specific 
gravity  is  10.4,  and  its  atomic  weight  is  181. 

Ores  of  the  Metal. — Tantalite,  FeO,  Ta205,  is  a  tantalate  of 
iron.  It  occurs  in  orthorhombic  crystals;  is  black  with  a  cin- 
namon-brown streak.  It  is  the  most  important  source  of  the 
tantalum  of  commerce. 

Manganotantalite,  MnO,  Ta2Os,  is  a  tantalate  of  manganese, 
in  which  manganese  has  displaced  the  iron  of  normal  tantalite 
to  a  considerable  extent,  if  not  entirely. 

Ixiolite  is  a  rare  tantalate  of  tin. 

Samarskite,  mentioned  under  Columbium,  is  a  rare  mineral 
rich  in  tantalum.  There  are  many  tantalates  of  the  rare  earth 
metals  known  in  mineralogy,  but  they  are  rare  minerals. 

Origin  of  the  Ores. — Tantalite,  like  its  associate,  columbite, 
occurs  as  a  primary  mineral  in  the  acid  intrusives,  as  the  granites 
and  pegmatites.  Some  of  the  rare  tantalates  are  decomposition- 
products  of  tantalite,  and  therefore  of  secondary  origin. 

Geographical  Distribution. — Tantalite  is  found  in  practically 
the  same  localities  as  columbite.  Massive  tantalite  has  been 
found  in  Coosa  County,  Alabama;  and  manganotantalite  of  ex- 
ceptional purity  in  western  Australia.  The  American  supply 
is  mainly  obtained  from  Scandinavia  and  Australia. 

Separation. — The  columbates  may  be  separated  from  the 
tantalates  by  fusion  with  HKS04  or  KOH,  and  treating  the  fused 
mass  with  HC1  and  metallic  zinc.  When  diluted  with  an  equal 
volume  of  water,  a  permanent  and  intense  blue  coloration  is 
obtained.  In  the  case  of  the  tantalates  thus  treated,  the  blue 
color  soon  disappears. 

Uses. — F.  L.  Hess  states  that  the  only  practical  use  to  which 
tantalum  is  put  is  in  making  filaments  for  incandescent  electric 
lamps.  More  than  twenty  thousand  20-candrle-power  incandes- 
cent electric  lamp  filaments  can  be  made  from  a  single  pound  of 
tantalum.  The  tantalum  lamps  used  in  America  are  manufac- 
tured from  imported  tantalum.  The  cost  of  the  metal  is  more 
than  $300  per  pound. 

The  metal  is  ductile,  malleable,  hard,  tough,  and  strongly 


THE  RARE  METALS  283 

resists  corrosion.     These  properties  ought  to  lead  to  new  uses  of 
commercial  significance. 

A  small  tonnage  of  tantalum-bearing  minerals  is  produced  by 
the  Western  Reduction  Company  of  Omaha,  Neb.  The  source 
of  the  ore  was  near  Keystone,  South  Dakota. 

Selenium 

Properties. — Selenium  is  a  non-metallic  element  closely  allied 
to  sulphur.  Its  association  with  copper,  silver,  lead,  mercury, 
bismuth  and  thallium,  together  with  its  relation  to  tellurium,  a 
semi-metallic  element,  has  led  to  its  consideration  in  this  work 
on  the  metallics.  Selenium  is  known  in  four  allotropic  modifi- 
cations: (1)  A  brick-red  amorphous  powder;  (2)  a  black  crystal- 
line powder;  (3)  in  dark  red  translucent  monoclinic  crystals; 
and  (4)  a  black,  shining,  brittle,  amorphous  mass.  It  is  a  con- 
ductor of  electricity.  The  conductivity  is  twice  as  great  in 
the  presence  of  light  as  in  the  dark.  The  melting-point  of  selen- 
ium is  217;  it  boils  at  680°  C.,  and  burns  with  a  blue  flame  to  Se02. 
Its  specific  gravity  varies  from  4.26  to  4.8,  and  its  atomic  weight 
is  79.2. 

Ores  of  Selenium. — Native  selenium,  Se. 

Selen-sulphur,  SeS,  an  orange-red  or  reddish-brown  mineral, 
consisting  of  mixtures  of  selenium  and  sulphur  in  unknown 
proportions. 

Selen-tellurium,  SeTe,  a  blackish-gray  mineral  with  metallic 
luster,  consisting  of  selenium  and  tellurium  in  the  ratio  of  2:  3. 

Clausthalite,  PbSe,  a  selenide  of  lead. 

Naumannite,  PbSe,  13Ag'2Se.  Another  variety  gives  5PbSe, 
Ag2Se;  a  third  variety  is  Ag2Se,  with  73.15  per  cent,  of  Ag. 

Guanajuatite,  Bi2Se3,  a  selenide  of  bismuth. 

Berzelianite,  Cu2Se,  a  selenide  of  copper. 

Lehrbachite,  (PbHg2)  Se,  a  selenide  of  lead  and  mercury. 

Eucairite,  Cu2Se,  Ag2Se,  a  selenide  of  copper  and  silver. 

Crookesite,  (Cu,  Ag,  Tl)2Se,  a  selenide  of  copper,  silver,  and 
thallium. 

Zorgite,  a  mixture  of  the  selenides  of  silver,  lead,  and  copper. 

Origin  of  the  Ores. — The  majority  of  the  selenides  are  primary 
minerals;  only  a  few  are  of  secondary  origin.  Native  selenium 
may  be  a  product  of  volcanic  emanation,  like  its  associate 
sulphur.  Selen-sulphur  occurs  in  crusts  with  sal-ammoniac  on 


284  ECONOMIC  GEOLOGY 

the  Vulcano  and  Lipari  Islands,  also  at  Kilauea  in  the  Hawaiian 
Islands.  Selen-tellurium  occurs  with  a  gangue  of  quartz  and 
barite  in  the  silver  veins  of  El  Plomo,  Honduras.  Zorgite  occurs 
in  argillaceous  schist  with  galenite  and  various  copper  minerals 
in  Thuringia. 

Character  of  Ore  Bodies. — Selenium  minerals  appear  in  metal- 
liferous veins  with  the  commoner  gangue  minerals,  and  as  crusts 
from  volcanic  emanation. 

Geographical  Distribution. — Selenium  minerals  are  rare  and 
not  widely  distributed.  In  America  they  are  largely  confined 
to  the  Cordilleran  section.  Selenides  appear  in  association 
with  the  gold  ores  of  the  Camp  Bird  mine  near  Ouray,  Colorado; 
in  the  Tonopah  gold  ores,  Nevada;  near  Marysville,  Utah;  and 
at  Clear  Lake,  California;  in  the  New  Zealand  gold  fields;  in 
Japan ;  and  in  the  Lipari  Islands. 

Geological  Horizon. — The  selenium  minerals  are  more  abun- 
dant in  the  terranes  associated  with  the  later  intrusives  of  the 
Cretaceous  and  Tertiary  ages  than  in  the  older  rocks. 

Method  of  Extraction. — Pyrite  containing  small  quantities  of 
selenium  is  often  used  in  the  manufacture  of  H2S04.  In  the 
roasting  of  the  pyrite,  the  selenium  is  oxidized  to  Se02,  and  is 
carried  off  with  the  sulphur,  which  is  oxidized  to  SO2.  The  selen- 
ium dioxide  is  deposited  as  a  solid  partly  in  the  flues  and  partly 
in  the  chambers.  These  deposits  are  gathered  and  boiled  with 
dilute  H2S04  and  HN03  or  KC1O3  to  oxidize  the  substance 
completely  to  H2Se04.  Strong  HC1  reduces  the  selenic  acid  to 
selenous  acid,  H2Se03.  Then  SO2  passed  through  the  selenous 
acid  precipitates  the  selenium  as  a  red  powder,  and  the  SO2  is 
oxidized  to  H2S04. 

Uses. — In  the  light,  selenium  is  a  good  conductor  of  electricity, 
and  on  account  of  this  peculiarity,  it  is  used  in  a  number  of 
electrical  devices.  It  has  been  used  in  telephoning  along  a  ray 
of  light,  and  in  transmitting  pictures,  photographs,  or  even 
sounds  to  a  considerable  distance  by  means  of  a  telephone  or 
telegraph  wire.  It  is  used  to  light  and  extinguish  gas-buoys 
automatically.  This  use  is  dependent  upon  the  fact  that  selenium 
is  a  non-conductor  of  electricity  in  the  dark  and  a  good  conductor 
in  the  light.  Selenium  is  used  also  in  measuring  the  quantity 
of  Rontgen  rays  in  therapeutiapc  plications. 

Economics. — The  production  of  selenium  from  year  to  year 
is  very  small.  It  is  sometimes  recovered  from  the  anode 


THE  RARE  METALS  285 

slimes  or  mud  where  it  is  left  with  the  gold,  silver,  etc.,  in  the 
electrolytic  refining  of  copper.  The  price  per  ounce  is  approxi- 
mately $2. 

Tellurium 

Properties. — Tellurium,  symbol  Te,  is  a  semi-metallic  element, 
the  least  abundant  of  the  sulphur  group.  It  is  brittle  and 
possesses  a  metallic  luster.  The  color  is  tin-white  or  bluish- 
white.  It  is  a  poor  conductor  of  both  heat  and  electricity. 
It  burns  with  a  blue  flame  to  Te02,  its  melting  point  is  446° 
C.,  its  hardness  is  2.2;  its  specific  gravity  is  6.25,  and  its  atomic 
weight  is  127.5. 

Ores  of  Tellurium. — Native  tellurium,  Te,  often  with  traces 
of  selenium  and  gold.  It  occurs  in  hexagonal  crystals,  also 
massive.  Selen-tellurium,  SeTe,  with  the  ratio  of  tellurium  to 
selenium  nearly  that  of  2  to  3.  Stutzite,  Ag4Te,  is  a  telluride  of 
silver  with  metallic  luster,  containing  22.5  per  cent,  of  Te  and 
75 . 5  per  cent,  of  Ag. 

Hessite,  Ag2Te,  is  another  telluride  of  silver,  with  36.7  per 
cent,  of  Te  and  63 . 3  per  cent,  of  Ag. 

Petzite,  (AgAu)2Te,  is  a  telluride  of  both  silver  and  gold. 
If  the  ratio  of  the  silver  to  the  gold  be  3:1,  the  analysis  would 
give  32.5  per  cent.  Te,  42  per  cent.  Ag,  and  25.5  per  cent.  Au. 

Sylvanite,  (AuAg)Te2,  is  a  telluride  of  gold  and  silver.  With 
a  ratio  of  1:1,  the  analysis  would  give  62.1  per  cent.  Te,  24.5 
per  cent.  Au,  and  13.4  per  cent.  Ag. 

Krennerite,  Ag2Te,  Au2Te3,  appears  to  be  an  admixture  of  the 
tellurides  of  gold  and  silver. 

Calaverite,  AuTe2,  is  a  telluride  of  gold,  although  a  part  of 
the  gold  is  often  displaced  by  silver.  These  tellurides  appear 
in  the  nature  of  alloys  rather  than  definite  compounds,  for 
both  tellurium  and  the  tellurides  of  gold  serve  as  a  precipitant 
for  gold. 

Altaite,  PbTe,  is  a  telluride  of  lead,  with  37.7  per  cent.  Te 
and  62.3  per  cent.  Pb. 

Coloradoite,  HgTe,  is  a  telluride  of  mercury,  with  38 . 5  per  cent. 
Te  and  61 . 5  per  cent.  Hg. 

Melonite,  Ni2Te3,  is  a  telluride  of  nickel,  with  76.2  per  cent. 
Te,  and  23.8  per  cent.  Ni. 

Rickardite,  Cu4Te3,  is  the  telluride  of  copper. 


286  ECONOMIC  GEOLOGY 

There  are  also  three  well-known  tellurides  of  bismuth: 
Tetradymite,  Bi2Te3;  Joseite,  Bi2Te;  Wehrlite,  Bi3Te2,  and  a 
sulphotelluride  of  bismuth,  Grunlingite,  Bi4TeS3. 

Tellurite,  TeO2,  the  dioxide,  is  an  oxidation-product  of 
tellurium. 

There  are  complex  tellurides  and  sulphotellurides  of  the 
precious  metals  that  need  not  be  mentioned  here. 

Origin  of  the  Ores. — The  most  of  the  tellurium  minerals  are 
of  primary  origin.  The  oxide,  the  tellurates  and  the  tellurites 
are  alteration-products. 

Character  of  the  Ore  Bodies. — The  tellurides  of  the  precious 
metals  occur  in  large  fissure-veins,  often  in  pockets  of  immense 
richness.  The  intrusive  granites  are  traversed  by  younger 
irruptives,  with  which  the  tellurides  are  connected.  H.  Ries 
states  that  they  are  not  found  in  contact  deposits.  (Calaverite 
occurs  as  a  coating  on  the  walls  of  fissures  at  Cripple  Creek, 
Colo.) 

Geographical  Distribution. — The  tellurides  of  the  metals  in 
the  United  States  are  largely  confined  to  the  Cordilleran  and 
Pacific  Coast  belts.  Altaite  has  been  found  in  Gaston  County, 
North  Carolina.  The  tellurides  are  found  abundantly  at  the 
Red  Cloud  mine,  Boulder  County,  Colorado;  the  Camp  Bird 
and  Torpedo-Eclipse  mines  in  Ouray  County;  in  many  mines  at 
Telluride  and  Cripple  Creek,  Colorado;  and  in  the  Stanislaus 
and  Golden  Rule  mines  in  Calaveras  County,  California.  The 
tellurides  occur  abundantly  in  western  Australia. 

Geological  Horizon. — A  little  tellurium  may  be  found  in  the 
mineral  deposits  of  the  older  geological  formations;  but  it  is 
far  more  abundant  in  association  with  the  Cretaceous  and 
Tertiary  formations  of  the  west. 

Uses. — The  aluminum  alloy,  Al2Te3  is  made  by  melting 
aluminum  and  throwing  in  from  time  to  time  small  pieces  of 
tellurium.  When  the  powdered  metals  are  heated  together, 
they  unite  with  great  violence.  The  uses  of  the  semi-metal 
tellurium  are  few. 

Economics. — The  output  is  small,  like  that  of  selenium.  A 
small  amount  of  tellurium  may  be  obtained  in  the  electrolytic 
refining  of  copper,  where  the  tellurium  is  deposited  in  the  anode 
slime  or  mud,  with  its  associates,  selenium,  gold,  and  silver. 


CHAPTER  X 

i 

ECONOMICS 

The  statistical  portion  of  this  book  has  been  left  for  the  final 
chapter  on  economics.  The  author  refrains  from  giving  in 
detail  the  output  of  the  different  metals  by  states  and  countries, 
and  would  refer  the  reader  for  such  data  to  the  carefully  compiled 
statistics  in  the  Mineral  Resources  of  the  United  States  and  in  the 
Mineral  Industry.  The  order  followed  in  this  chapter  in  the 
discussion  of  the  economic  conditions  surrounding  the  different 
industries  and  the  output  of  the  different  metals  is  the  same  as 
that  given  in  the  main  body  of  the  work. 

GOLD 

Production  in  the  United  States. — The  output  of  gold  in  the 
United  States  during  the  present  century  has  been  fairly  steady. 
A  decrease  of  about  $4,000,000  was  suffered  in  1903.  A  similar 
decrease  was  experienced  in  1907.  This  was  followed  by  a  third 
decrease  in  1910,  and  by  a  large  decrease  in  1912. 

The  banner  year  was  reached  in  1909  when  the  production 
was  $99,673,400.  This  large  production  was  due  to  several 
causes:  (1)  The  tendency  to  increased  production  which  began 
in  1907.  (2)  To  a  small  degree  to  the  closing  of  many  mines 
in  the  base  metal  camps  which  curtailed  the  output  of  lead, 
copper  and  zinc,  and  increased  the  output  of  gold  by  the  shifting 
of  labor  to  the  placer  deposits.  (3)  The  fundamental  cause 
of  the  large  prosperity  in  the  gold  mining  industry  is  the  fixed 
and  limitless  demand  for  the  yellow  metal. 

According  to  H.  D.  McCasky  of  the  U.  S.  Geological  Survey, 
the  output  of  gold  for  1912  was  $91,685,168.  In  1911  it  was 
$96,890,000.  The  decrease  is  ascribed  mainly  to  Nevada  where 
there  was  a  falling  off  in  the  annual  production  of  nearly 
$4,000,000,  chiefly  from  Goldfield,  but  to  a  smaller  degree  also  to 
Nation  and  Seven  Troughs  camps.  The  Goldfield  mines  pro- 
duced a  larger  tonnage  of  ore,  but  of  lower  grade  than  in  the 

287 


288  ECONOMIC  GEOLOGY 

preceding  year.  The  production  was  delayed  at  Seven  Troughs 
by  a  cloudburst  in  July  and  the  mill  at  National  was  burned  in 
September.  On  the  other  hand  there  was  an  increased  production 
in  the  Manhattan,  Fairview,  and  Round  Mountain  districts. 

In  Colorado  also  there  were  several  fluctuations  in  the  gold 
mining  camps.  The  San  Juan  district,  which  includes  the  counties 
of  Dolores,  La  Plata,  Ouray,  San  Juan,  and  San  Miguel,  showed 
a  decrease  of  about  $1,000,000.  This  came  largely  from  the 
Camp  Bird  mine  on  Sneffels  creek.  The  Cripple  Creek  district 
increased  its  output  by  nearly  $400,000,  due  in  part  to  the 
successful  drainage  by  the  Roosevelt  tunnel.  Montana,  Utah 
and  Washington  each  showed  a  decreased  production. 

The  gold  mining  industry  in  South  Dakota  gave  the  largest 
output  in  the  history  of  the  state,  the  increase  being  about 
$400,000  over  the  output  of  1911,  due  largely  to  activities  in  the 
Homestake  mines.  The  large  hydroelectric  plant  of  the  company 
owning  these  mines  was  completed  and  put  into  operation  in 
1912. 

California  retains  the  rank  of  the  first  producer  which  position 
she  wrested  from  Colorado  in  1911.  Nevada,  Alaska  and  South 
Dakota  are  also  large  producers. 

Gold  dredging  was  especially  active  in  California  and  Alaska 
where  increased  dredging  capacity  was  added.  The  120  dredges 
in  operation  in  10  states  including  Alaska  produced  more  than 
$10,000,000  of  gold. 

According  to  the  Geological  Survey,  in  1911,  the  gold  and 
silver  mills  produced  53.8  per  cent,  of  the  output,  the  placers 
24  per  cent.,  and  the  large  smelting  plants  22  per  cent.  Of  the 
product  from  the  gold  and  silver  mills  26 . 1  per  cent,  was  produced 
by  cyanidation,  23.9  per  cent,  by  amalgamation,  and  3.8  per 
cent,  by  chlorination.  Dredging  alone  gave  10.9  per  cent. 

During  the  past  few  years  there  has  been  a  general  decline  in 
the  prospecting,  and  no  notable  discoveries  of  new  ore  bodies 
or  deposits  that  seem  likely  to  give  immediate  material  increase 
to  the  annual  output  of  gold  have  been  effected.  The  ore  bodies 
in  some  of  the  large  camps,  as  at  Goldfield,  already  show  a  diminu- 
tion in  the  value  per  ton  of  ore  mined. 

Imports  and  Exports. — According  to  estimates  made  for  the 
Survey  by  the  Bureau  of  Foreign  and  Domestic  Commerce,  the 
imports  of  gold  for  1912  were  valued  at  $61,400,000.  The 
exports  for  the  same  year  were  valued  at  $48,600,000,  The 


ECONOMICS  289 

excess  of  the  imports  over  the  exports  for  1912  was  $12,800,000 
which  forms  a  striking  contrast  with  the  conditions  in  1909 
when  the  exports  exceeded  the  imports  by  $88,793,855.  The 
imported  gold  in  both  ore  and  bullion  came  from  Mexico, 
Canada,  England,  France,  Central  and  South  America.  The 
exports  consisted  of  refined  bullion  and  coin  and  went  largely  to 
France,  South  America,  Canada,  and  Japan  with  smaller  ship- 
ments to  the  West  Indies. 

World's  Production. — According  to  Frederick  Hobart,  the  gold 
production  of  the  world  for  1912  exceeded  that  of  any  previous 
year.  It  was  an  increase  of  $10,000,000  or  2.2  per  cent,  over 
the  output  of  1911.  The  gain  in  the  Transvaal  alone  was 
approximately  $18,225,000.  The  mines  of  Rhodesia  and  West 
Africa  also  showed  notable  gains.  The  total  African  production 
was  $21 1 ,789,000  while  the  Transvaal  alone  produced  $  188,285,000. 

The  Asiatic  mines,  especially  those  in  the  Kolar  district  in 
British  India,  increased  their  annual  output.  Australasia, 
which  at  one  time  produced  nearly  one-third  of  the  world's 
total  output  of  gold,  now  produces  only  12.1  per  cent,  of  the 
total.  Western  Australia  is  the  largest  producer  in  Australasia, 
The  steady  decrease  in  the  value  of  the  ore  mined  and  the  fact 
that  no  new  gold-bearing  ore  bodies  are  being  discovered  are 
matters  of  moment  in  the  consideration  of  the  future  of  the 
industry.  New  Zealand  also  records  a  lessened  production  due 
to  labor  difficulties  which  it  is  expected  will  not  materially  affect 
the  output  of  1913.  The  decline  in  Russia  was  due  also  to  labor 
difficulties  and  to  the  shortage  of  water  in  many  of  the  important 
places,  notably  the  Lena  Gold  Mining  Company  which  in  recent 
years  has  been  the  largest  producer  of  Siberia.  A  decline  was 
recorded  also  for  Mexico  which  is  attributed  to  the  disturbed 
political  condition  of  the  country. 

The  total  output  of  gold  for  1912  was  $469,618,083.  There 
has  been  a  steady  annual  increase  in  the  production  of  gold  for 
the  last  14  years,  save  in  1910  when  there  was  a  decrease  of 
approximately  $5,000,000.  Since  1893  the  world's  annual 
production  of  the  yellow  metal  has  increased  $311,180,532. 

SILVER 

Price  and  Production. — The  conditions  surrounding  the  silver 
mining  industry  from  1908  to  1912  were  not  altogether  satis- 
factory. The  average  price  for  silver  in  1908  was  53  cents  per 

19 


290  ECONOMIC  GEOLOGY 

Troy  ounce;  in  1909  it  was  52  cents;  in  1910,  54  cents;  in  1911, 
53  cents;  in  1912,  it  was  60.9  cents.  While  the  lower  prices 
for  silver  obtained,  several  large  smelters  in  Utah  and  Colorado 
were  partly  closed  or  operated  on  a  reduced  capacity.  This 
held  especially  true  at  Leadville  where  the  ores  are  low  grade. 

The  conditions  operating  against  a  large  output  of  silver  from 
1908  to  1911  were:  (1)  The  low  price  of  silver  for  commercial 
purposes.  (2)  The  low  price  of  copper,  lead  and  zinc  with  which 
silver  ores  are  so  often  associated.  (3)  The  failure  of  India  to  buy 
as  much  silver  as  usual,  a  condition  that  was  partly  offset  by  a 
larger  purchase  on  the  part  of  China.  (4)  The  increased 
production  in  Canada  due  to  the  more  recently  discovered 
districts  of  Cobalt,  South  Lorrain  and  Gowganda. 

The  estimates  of  the  United  States  Geological  Survey  and  the 
Bureau  of  the  Mint  indicate  a  domestic  silver  production  for 
1912  of  62,369,974  fine  ounces,  valued  at  $37,982^414.  This 
represents  the  largest  annual  output  of  silver  for  the  last  twenty 
years,  although  it  does  not  represent  the  largest  value  of  the 
period.  The  reports  from  the  west  indicate  that  when  the 
statistics  are  finally  completed  the  output  will  approximate 
64,000,000  oz.  If  it  reaches  that  figure  it  will  represent  the 
largest  output  in  the  history  of  the  industry. 

The  conditions  favoring  this  increase  for  1912  were:  (1)  A 
higher  price  for  the  metal  for  commercial  purposes;  (2)  a  year  of 
general  business  prosperity;  (3)  a  liberal  buying  in  all  metals 
during  the  year;  (4)  large  purchases  of  silver  on  the  part  of 
India  and  (5)  a  notable  increase  in  the  output  of  copper  ores, 
especially  those  of  Butte,  Montana,  which  contain  considerable 
silver,  and  of  argentiferous  lead  ores,  especially  of  the  Tintic 
and  Park  City  districts  of  Utah;  the  Pioche  district  of  Nevada; 
the  San  Juan,  Leadville  and  Aspen  districts  of  Colorado.  There 
was  a  small  decrease  in  the  output  of  the  Coeur  d'Alene  mining 
district  in  Idaho  due  to  lower  grade  of  ore  than  formerly  mined. 

According  to  the  Mineral  Resources  of  the  United  States  for 
1911,  Nevada  was  the  first  producer  of  silver  with  a  value  of 
$6,987,839  followed  by  Utah  with  a  value  of  $6,611,107  and  Mon- 
tana with  $6,352,154  .  In  1912  the  outputs  in  Troy  ounces  were 
as  follows:  Nevada,  13,042,118;  Utah,  12,795,072;  Montana, 
12,338,589. 

Imports  and  Exports. — According  to  estimates  made  by  the 
Bureau  of  Foreign  and  Domestic  Commerce  the  imports  of  silver 


ECONOMICS  291 

for  1912  were  valued  at  $47,800,000.  The  exports  for  the  same 
year  were  valued  at  $70,272,000,  or  $22,472,000  in  excess  of 
the  imports.  The  imports  were  largely  silver  ore  and  bullion 
from  Mexico  and  Canada.  The  exports  were  almost  wholly  in 
refined  bullion  and  coin  and  went  chiefly  to  the  United  Kingdom, 
although  large  amounts  were  shipped  to  France  and  China,  with 
smaller  amounts  to  British  India. 

World's  Silver  Production. — The  silver  production  of  the 
world  in  fine  ounces  for  1912  as  given  by  the  Engineering  and 
Mining  Journal  is  as  follows: 

Mexico 76,500,000 

United  States 62,369,903 

Canada 35,250,000 

Australasia 17,950,000 

Other  countries 37,500,000 


Total 229,569,903 

As  will  be  seen  in  the  table  given  above  Mexico  still  holds  the 
position  of  the  first  producer  and  the  United  States  the  second. 
By  a  comparison  of  these  figures  with  those  of  1911  it  will  be 
seen  that  the  production  of  Mexico  decreased  approximately 
3,000,000  oz.,  while  that  of  the  United  States  increased  approxi- 
mately 2,000,000.  The  remarkable  increase  during  the  past 
three  years  is  in  Canada  where  the  production  was  more  than 
13,000,000  oz.  greater  in  1912  than  in  1909.  The  one  field  giving 
rise  to  this  condition  is  Cobalt  where  large  supplies  of  silver  ore 
have  been  opened  in  recent  years.  This  field  is  somewhat 
augmented  by  outputs  from  the  South  Lorrain  and  Gowganda 
districts. 

PLATINUM 

Production. — Some  platinum  of  recent  years  has  been  pro- 
duced at  the  placer  mines  in  Butte,  Humboldt,  Siskiyou,  Trinity, 
Calaveras,  Sacramento  and  Del  Norte  Counties,  California, 
together  with  a  small  amount  from  western  Oregon.  Three- 
fourths  of  all  the  domestic  platinum  comes  from  Butte  County. 

The  most  noteworthy  event  in  the  platinum  industry  during  the 
present  century  is  the  discovery  of  the  comparatively  new  mineral 
sperrylite,  the  arsenide  of  platinum,  PtAs2,  which  occurs  in  the 
nickel-bearing  ores  of  Sudbury,  Ontario,  and  in  the  Rambler 
mine  of  Wyoming. 


292  ECONOMIC  GEOLOGY 

Importance  is  also  attached  to  the  discovery  of  platinum  in 
association  with  several  copper  minerals,  as  covellite,  the  sulphide 
of  copper,  CuS.  This  result  may  lead  to  the  discovery  of 
platinum  in  other  members  of  the  copper  group. 

The  average  price  paid  for  platinum  in  1912  was  $45.55  per 
Troy  ounce  as  compared  with  $43.12  in  1911  and  $32.70  in  1910. 
With  this  higher  price  for  platinum  it  is  rational  to  expect  a 
persistent  search  for  platinum  ores  in  the  placer  gravels  of 
serpentine  rocks;  in  the  members  of  the  copper  group,  and  in  the 
nickeliferous  pyrrhotites. 

The  demand  for  platinum  is  increasing  faster  than  the  supply. 
The  newer  requirements  in  the  electrical  and  automobile-engine 
industries  absorb  the  metal  and  remove  it  from  the  market 
entirely.  The  same  is  largely  the  case  in  the  jewelry  industry, 
while  the  metal  used  in  making  chemical  ware  is  largely  returned 
in  the  form  of  scrap  platinum  for  manufacture. 

The  imports  of  platinum  for  1912  were  valued  at  $3,634,738. 
No  platinum  seems  to  have  been  re-exported. 

Russia  is  the  world's  chief  producer  of  platinum.  The  metal 
comes  from  the  Siberian  side  of  the  Urals.  The  production  for 
1912  is  estimated  at  310,000  ounces.  Colombia  is  the  second 
producer  with  an  output  estimated  at  12,000  ounces.  A  small 
amount  of  platinum  is  derived  also  from  Canada,  New  South 
Wales,  Borneo  and  Sumatra. 


LEAD 

Production. — The  value  of  the  output  in  the  lead  industry 
has  risen  from  $23,280,200  in  1901  to  $43,280,460  in  1912.  The 
increment  of  increase  has  not  been  steady.  In  1908  the  produc- 
tion fell  32. 56  per  cent,  below  that  of  1907.  The  lead  produced 
in  the  United  States  is  derived  from  various  sources  and  receives 
different  names,  dependent  upon  its  source. 

Primary  lead  signifies  lead  that  has  been  produced  directly 
from  its  ores.  Secondary  lead  is  derived  from  scimmings, 
drosses,  old  metal,  alloys,  as  babbitt,  solder,  and  type  metal. 
The  recovery  of  lead  by  refining  these  materials  constitutes  an 
integral  portion  of  the  lead  industry.  The  business  is  mostly 
carried  on  by  the  small  refineries  scattered  over  the  United 
States,  but  the  large  smelters  and  refineries  working  primary 
lead  frequently  incorporate  material  from  secondary  sources. 


ECONOMICS  293 

Soft  lead  represents  the  production  of  the  smelters  in  the 
Mississippi  Valley  where  the  ores  are  almost  free  from  silver. 
Only  one  of  the  smelters  in  this  district  desilverizes  its  lead. 
However,  a  considerable  quantity  of  soft  lead  ores  have  been 
annually  smelted  by  various  silver-lead  smelters.  A  little  soft 
lead  ore  is  annually  derived  from  Washington  and  other  western 
states. 

Refined  lead  embraces  all  of  the  desilverized  lead  produced  in 
this  country  and  the  pig  lead  recovered  from  the  Mississippi 
Valley  lead  industry. 

Antimonial  lead,  or  hard  lead,  is  derived  from  the  treatment  of 
the  gold  and  silver  ores  bearing  antimony.  The  antimony 
combines  with  the  lead  as  antimonial  lead.  The  two  metals  are 
never  separated,  and  there  is  a  large  demand  for  this  product. 

There  are  two  lead  pigments  produced  directly  from  various 
plumbiferous  ores,  namely,  sublimed  white  lead  and  sublimed 
blue  lead.  The  former  consists  of  lead  sulphate  75  per  cent., 
lead  oxide  20  per  cent.,  and  zinc  oxide  15  per  cent.  The  latter 
consists  of  lead  sulphate  varying  from  50  to  53  per  cent.,  lead 
oxide  41  to  38  per  cent.,  together  with  small  proportions  of  lead 
sulphide,  lead  sulphite,  and  zinc  oxide.  Zinc-lead  oxide  con- 
tains from  46  to  50  per  cent,  of  lead  sulphate,  frem  32  to  46  per 
cent,  of  zinc  oxide,  and  a  small  amount  of  zinc  sulphate. 
Leaded  zinc  oxide  varies  from  4  to  20  per  cent,  in  its  lead  sulphate 
content,  while  the  remainder  is  zinc  oxide  together  with  a  small 
proportion  of  zinc  sulphate.  The  total  lead  content  from 
domestic  ores  averages  between  7000  and  8000  short  tons. 

Missouri  is  the  first  producer  of  lead  followed  by  Idaho,  Utah, 
and  Colorado  in  the  order  of  their  importance.  The  United 
States  produced  approximately  twice  as  much  lead  as  any  other 
country,  followed  by  Spain,  Germany  and  Mexico  each  of  which 
produces  more  than  100,000  metric  tons. 

MERCURY 

Production. — The  unit  of  measure  for  mercury  is  different 
from  that  of  the  other  metals^  The  liquid  metal  is  put  up  in 
flasks.  Each  flask  contains  75  Ib.  The  market  at  San  Francisco 
determines  the  price.  The  average  price  per  flask  for  1912  was 
$42.04.  This  represents  a  total  value  of  $1,057,180  for  the 
1912  production. 


294  ECONOMIC  GEOLOGY 

According  to  H.  D.  McCaskey  the  gain  of  3891  flasks  over 

1911  shows  a  larger  increase  than  was  generally  expected,  but 
he  does  not  think  it  implies  a  corresponding  increase  in  the 
output  of  1913.     A  gradual  decline  in  the  output  of  some  of  the 
larger  ore  bodies  and  possibly  unfavorable  market  conditions 
and  prospects  tend  toward  a  reduction  of  the  output. 

The  output  of  1912  was  the  largest  in  California  since  1905. 
The  increase  was  due  to  two  factors:  (1)  The  satisfactory 
product  of  the  New  Guadalupe  mine  in  Santa  Clara  county. 
(2)  To  increased  output  from  several  other  mines.  The  New 
Idria  mines  in  San  Benito  County  are  the  largest  producers  in 
America  and  in  fact  produce  nearly  one-half  of  the  California 
mercury.  The  output  of  these  mines  for  1912  was  slightly  less 
than  in  1911  because  attention  was  paid  to  development  work 
rather  than  to  increased  production  on  account  of  low  prices. 
Ore  reserved  for  treatment  when  prices  were  at  a  higher  level 
seemed  preferable.  Sixteen  mines  were  producers  for  the  year 

1912  in  California. 

Texas  is  also  a  producer  of  mercury.  According  to  W.  B. 
Phillips  there  were  no  material  changes  in  the  industry  during 
the  year  1912.  The  Chisos  Mining  Company  carried  their 
explorations  into  the  Buda  limestone  that  underlies  the  Eagle 
Ford  shales  and  found  about  the  same  quality  of  ore  as  in  the 
overlying  bituminous  shales.  A  furnace  has  been  constructed  on 
the  property  to  handle  a  larger  tonnage  of  lower  grade  ore  rather 
than  a  smaller  tonnage  of  high  grade  ore.  In  the  Terlingua 
district  the  larger  percentage  of  the  ore  has  come  from  the  hard, 
dense  limestone  of  the  Edwards  formation  which  has  yielded 
ore  of  extreme  richness  at  comparatively  shallow  depths.  It 
is  Phillips'  belief  that  the  future  of  the  mercury  industry  in  Texas 
will  be  more  intimately  connected  with  the  bituminous  shales 
than  with  the  associated  limestones. 


BISMUTH 

Production. — The  production  of  metallic  bismuth  in  the  United 
States  is  very  small.  The  years  1902,  1903,  1907,  report  no  out- 
put whatever.  The  United  States  Metals  Refining  Company 
produces  a  small  amount  of  bismuth  as  a  by-product  at  its 
electrolytic  lead  refinery  at  Grasselli,  Indiana.  The  bismuth  is 
obtained  in  the  anode  muds  of  lead  bullion.  The  most  of  the 


ECONOMICS  295 

bismuth-bearing  ores  come  from  the  Tintic  district,  Utah,  and 
are  smelted  at  Bingham  Junction. 

Many  tungsten  ores  are  bismuth  bearing.  The  latter  metal 
may  be  recovered  as  a  by-product  when  reducing  the  tungsten. 
Some  bismuth  is  recoverable  in  the  electrolytic  copper  refineries. 

According  to  F.  L.  Hess  in  1911  one  lot  of  bismuth-bearing 
ore  was  produced  at  the  Comstock  mine,  La  Plata,  La  Plata 
County,  Colorado.  This  ore  contains  from  6  to  8  per  cent,  of 
bismuth  but  was  sold  for  its  gold  and  silver  content.  A  smaller 
amount  of  higher  grade  bismuth  ore  was  mined  near  Tularosa, 
New  Mexico. 

The  average  price  for  metallic  bismuth  for  the  year  was 
$1 . 72  per  pound.  The  value  of  imported  bismuth  for  several 
years  has  been  between  $300,000  and  $400,000.  The  larger 
part  of  the  supply  of  the  crude  metal  comes  from  Bolivia,  where 
the  Aramayo  Francke  Mines,  Ltd.,  is  one  of  the  large  producers. 
The  crude  metal  is  shipped  to  Europe  for  subsequent  refining. 
According  to  the  Engineering  and  Mining  Journal  there  will  be 
one  new  producer  of  bismuth  in  1913,  viz.,  The  American 
Smelting  and  Refining  Company  which  has  completed  its  plant 
at  Omaha,  Nebraska. 

COPPER 

Production. — The  production  of  copper  in  the  United  States 
shows  a  steady  increase.  The  only  large  reduction  in  any 
single  year  came  in  1907  as  a  result  of  the  general  financial  de- 
pression. The  output  of  copper  for  1912  is  the  largest  ever 
recorded.  The  copper-producing  states,  Arizona,  Michigan, 
Utah,  Colorado,  New  Mexico,  and  Alaska,  each  exceeded  all 
former  records.  Montana  and  Tennessee  nearly  equalled  their 
banner  output. 

There  is  no  close  competitor  to  the  United  States  in  the  produc- 
tion of  the  red  metal.  In  fact  the  United  States  produces  more 
than  50  per  cent,  of  the  world's  supply  of  copper.  The  increased 
output  is  due  to  several  causes.  (1)  The  discovery  and  the 
opening  of  many  new  mines.  (2)  The  working  of  old  mines  to 
their  full  capacity.  (3)  The  extension  of  electrical  works  of  all 
kinds.  (4)  The  construction  of  new  electrical  roads.  (5)  The 
substitution  of  electricity  on  existing  roads.  (6)  The  present 
period  of  high  and  profitable  prices. 


296  ECONOMIC  GEOLOGY 

According  to  B.  S.  Butler  of  the  U.  S.  Geological  Survey  the 
output  of  blister  and  Lake  copper  for  1912  was  1,249,000,000 
lb.,  which  at  an  average  price  of  16  cents  per  pound  amounts  to 
approximately  $200,000,000.  The  figures  of  the  Copper  Pro- 
ducers' Association  indicate  a  production  of  refined  copper  from 
all  sources,  domestic  and  foreign,  of  approximately  1,500,000,000 
lb.  for  1912. 

The  average  price  for  electrolytic  copper  for  1912  was  highly 
satisfactory,  averaging  about  16  cents  as  compared  with  12.5 
cents  per  pound  in  1911. 

According  to  the  Bureau  of  Statistics  the  imports  of  copper 
for  1912  approximated  to  404,721,323  lb.,  which  is  70,000,000 
lb.  in  excess  of  the  importation  of  1911.  The  metal  is  imported 
in  the  forms  of  old  copper,  pigs,  bars,  ingots,  plates,  etc.  The 
exports  for  1912  were  approximately  750,000,000  lb. 

Arizona  holds  the  rank  of  the  first  producer.  The  state  also 
holds  the  enviable  record  of  furnishing  a  larger  production  than 
that  ever  recorded  by  any  state  for  a  single  year.  The  output 
approximated  350,000,000  lb.,  and  came  largely  from  the  Bisbee, 
Morenci-Metcalf,  and  Globe-Miami  districts. 

Montana  was  the  second  producer  with  an  output  exceeding 
300,000,000  lb.  As  in  previous  years  the  output  came  largely 
from  the  Butte  district.  Michigan  ranks  third  as  a  copper 
producer.  The  product  came  largely  from  the  old  producers 
stimulated  by  the  high  prices  for  the  metal.  Utah,  Nevada, 
California,  New  Mexico  and  Alaska  are  noteworthy  producers. 
The  output  in  Alaska  came  largely  from  the  Copper  River  and 
Prince  William  Sound  districts  although  southeastern  Alaska 
contributed  somewhat  to  the  supply. 

The  total  output  of  copper  for  the  world  for  1912,  as  estimated 
by  the  Engineering  and  Mining  Journal,  was  1,004,844  metric 
tons.  Of  this  amount  the  United  States  produced  536,747  tons, 
Mexico  71,982  tons,  Spain  and  Portugal  58,000  and  Japan 
54,000. 

CADMIUM 

Production. — The  output  of  cadmium  in  the  United  States 
is  small,  due  to  the  fact  that  its  chief  ore  is  limited  in  quantity 
and  distribution,  and  also  to  the  limited  demand  for  the  metal. 

According  to  C.  E.  Siebenthal,   metallic  cadmium  has  been 


ECONOMICS  297 

recovered  in  the  United  States  since  1907  by  only  one  company 
until  the  latter  part  of  1910.  Since  that  time  there  have  been 
two  producers.  A  small  quantity  of  the  pigment,  cadmium 
sulphide,  is  also  produced.  The  metal  may  be  derived:  (1) 
From  the  fractional  distillation  of  zinc  ores;  (2)  recovered  as  a 
by-product  in  the  manufacture  of  lithopone;  and  (3)  by  the 
dry  distillation  or  electrolysis  of  the  slimes  formed  in  the 
manufacture  of  zinc  chloride. 

The  chief  output  of  cadmium  comes  from  the  zinc-producing 
districts  of  Silesia,  where  the  metal  is  recovered  as  a  by-product 
in  the  manufacture  of  zinc.  In  England  a  small  amount  of 
cadmium  has  been  recovered  in  the  purification  of  the  solution 
of  zinc  sulphate  in  the  manufacture  of  lithopone. 

A  small  amount  of  metallic  cadmium  is  annually  imported 
in  the  form  of  sticks.  Also  a  small  amount  of  the  sulphide  under 
the  name  of  cadmium  yellow.  The  total  average  value  of  these 
products  is  less  than  $5000  per  annum. 

ARSENIC 

There  was  no  production  of  white  arsenic  in  the  United  States 
prior  to  1901.  Among  the  new  industries  that  have  been  devel- 
oped recently  is  the  manufacture  of  white  arsenic  as  a  by- 
product in  the  treatment  of  other  ores.  A  pioneer  in  this 
industry  was  the  Puget  Sound  Reduction  Company  which  recov- 
ered arsenic  from  the  Monte  Cristo,  Washington,  ores.  The 
Everett  smeltery  at  Everett,  Washington,  the  Washoe  plant 
at  Anaconda,  Montana,  and  the  United  Smelting  Company  at 
Midvale,  Utah,  are  among  the  producers  of  this  commodity. 

The  production  suffered  a  decline  in  1904,  1909,  and  in  1912. 
The  output  for  1912  was  5,852,000  Ib.  in  comparison  with 
6,162,000  Ib.  in  1911. 

The  imports  of  arsenic  are  not  heavy.  About  150  tons  of  red 
arsenic,  As2S2,  and  from  50  to  75  tons  of  metallic  arsenic  and  lead- 
arsenic  alloys  meet  the  demand  for  these  products.  Germany, 
France,  United  Kingdom,  Spain,  in  the  order  of  their  output, 
produce  a  total  of  between  2000  and  3000  metric  tons  of  white 
arsenic  per  annum. 

ANTIMONY 

Antimony  for  consumption  in  the  United  States  is  largely 
derived  from  four  sources:  (1)  Hard  lead  obtained  in  the 


298  ECONOMIC  GEOLOGY 

smelting  of  foreign  and  domestic  ores;  (2)  imported  regulus  or 
metal;  (3)  imported  antimony  ores;  and  (4)  domestic  ores. 
According  to  the  Engineering  and  Mining  Journal  several  carloads 
of  ore  were  mined  in  1912  in  Utah,  and  successfully  treated  to 
recover  the  antimony  content,  but  even  at  the  present  price  of 
the  metal,  the  mines  are  burdened  with  too  expensive  transporta- 
tion to  be  profitable,  and  they  have  suspended  production. 
The  bulk  of  antimony  used  in  the  United  States  must  therefore 
be  imported.  The  duty  on  the  crude  metal  is  1J  cents  per 
pound  and  1  cent  per  pound  on  the  metal  in  ore. 

The  average  price  for  metallic  antimony  in  1912  was  8.26 
cents  per  pound.  The  imports  of  antimony  in  all  forms  for  the 
first  10  months  of  the  year  were  8,848,874  lb.,  which  was  an 
increase  of  355,370  lb.  over  1911.  The  antimony  oxide  produced 
during  the  year  was  practically  all  manufactured  from  Chinese 
needle  antimony. 


TIN 

The  production  of  tin  in  the  United  States  is  a  matter  of 
perennial  interest  because  of  the  peculiar  deficiency  of  tin  deposits 
and  the  large  domestic  consumption.  The  chief  interest  sur- 
rounding the  tin  industry  during  the  present  century  lies  in  the 
construction  of  a  mill  and  smelter  for  the  production  of  the  metal 
by  the  El  Paso  Tin  Mining  and  Smelting  Company  in  Texas. 
(2)  The  Pahasa  Mining  Company  has  opened  the  old  shaft  of 
the  Harney  Peak  Tin  Company  of  the  Southern  Black  Hills 
in  South  Dakota,  and  sampled  the  ore  bodies  to  ascertain  their 
value.  (3)  The  increasing  output  of  tin  in  Alaska. 

The  tin  for  domestic  consumption  comes  from  three  sources: 
(1)  domestic  primary  tin,  (2)  secondary  tin,  (3)  imports. 

According  to  F.  L.  Hess  the  output  of  tin  in  Alaska  for  1911 
was  61  tons  of  metallic  tin  valued  at  $52,409.  The  vast  majority 
of  this  came  from  the  placers  on  Buck  Creek.  A  small  amount 
came  from  the  placers  of  Tofty  Gulch,  on  Sullivan  Creek,  between 
Fairbanks  and  the  mouth  of  Tanana  River.  The  tin  mine  near 
El  Paso,  Texas,  produced  5  tons  of  metallic  tin.  The  entire 
output  of  the  United  States  for  1911  was  values  at  $56,635. 

According  to  J.  P.  Dunlop  the  secondary  recoveries  of  tin 
form  the  most  important  domestic  source  of  supply.  Tin  is 
recovered  from  the  various  alloys  containing  the  metal  as 


ECONOMICS  299 

babbitt,  bronze,  solder,  etc.  It  includes  the  tin  content  of 
products  made  by  several  plants  from  tin  scrap  as  tin  oxide, 
putty  powders,  but  mainly  tin  chloride.  The  largest  recovery 
of  tin  is  made  from  the  scruff  and  drosses  that  are  formed  in  the 
manufacture  of  tiii  and  terne  plate.  Practically  no  clean  scrap 
tin  plate  is  wasted.  A  large  quantity  of  tin  is  recovered  in  the 
form  of  tin  powder  by  electrolytic  treatment.  Lesser  sources 
of  tin  are  tin  foil,  block-tin  pipe,  and  old  tin  cans.  The  amount 
of  secondary  tin  recovered  from  all  sources  in  1911  was  valued 
at  $12,353,040. 

The  total  value  of  the  imports  of  tin  for  1911  amounted  to 
$43,584,219,  which  exceeds  the  value  of  the  importation  for  any 
other  year. 

The  Federated  Malay  States  produces  more  tin  than  all  the 
other  countries  of  the  world  combined.  The  order  of  the  states 
in  the  production  is  as  follows :  Perak,  Selangor,  Negri  Sembilan, 
and  Pahang.  Bolivia  is  the  second  producer  and  Banka  the 
third.  The  shipments  from  Banka  are  to  Holland.  The 
output  of  Cornwall,  England,  is  about  5000  short  tons  per 
annum. 


•    IRON 

According  to  E.  F.  Burchard  of  the  United  States  Geological 
Survey  the  production  of  iron  ores  for  1912  was  between  54,500,- 
000  and  57,500,000  tons.  The  quantity  represents  an  increase  of 
approximately  30  per  cent,  over  the  output  of  1911  which  was 
43,550,633  tons.  A  high  record  in  the  output  of  iron  ores  was 
established  in  1910.  When  it  aggregated  56,889,734  long  tons. 

The  percentage  of  red  and  specular  hematite  mined  year  after 
year  is  increasing.  More  than  90  per  cent,  of  the  iron  ore  mined 
for  1912  came  from  these  two  varieties  of  hematite.  Limonite 
and  magnetite  in  about  equal  proportions  contributed  the 
remainder  save  for  a  very  small  percentage  of  siderite.  This 
mineral  ordinarily  contributes  in  America  about  0.1  per  cent. 

The  Lake  Superior  district  produces  more  than  80  per  cent, 
iron  ore.  These  ores  not  only  supply  the  furnaces  of  the  Central 
West  but  also  find  their  way  east  of  the  Atlantic  Coast. 

The  production  of  the  Birmingham  district  in  Alabama  was 
also  largely  increased  in  1912.  For  this  increase  the  Clinton 
hematite  of  the  Red  Mountain  group  was  largely  responsible. 


300  ECONOMIC  GEOLOGY 

The  production  of  Tennesee,  North  Carolina  and  Virginia 
remained  about  the  same  as  in  1911. 

The  heavy  demand  for  iron  ores  in  1912  increased  mining 
activities  in  New  York,  New  Jersey,  and  Pennsylvania.  In 
these  states  several  new  mines  were  opened,  some  old  mines 
were  reopened,  and  some  improvements  were  made  in  the  con- 
centration of  the  ore  to  make  it  more  available  for  the  furnaces. 
The  largest  activity  was  in  the  Champlain  district  in  the  vicinity 
of  Port  Henry,  Mineville  and  Dannemora. 

Imports  and  Exports. — The  imports  of  iron  ore  for  the  first  ten 
months  of  1912  were  1,741,607  tons.  Of  this  amount  more  than 
1,000,000  tons  came  from  Cuba.  Other  contributors  in  the 
order  of  their  importance  are  Sweden,  Newfoundland,  Canada, 
Spain,  and  Venezuela.  The  exports  of  iron  ore  for  the  same 
period  exceeded  1,000,000  tons.  The  ores  were  mainly  derived 
from  the  Lake  Superior  district  and  were  shipped  to  Canadian 
furnaces. 

The  Bureau  of  Statistics  gives  the  value  of  the  exports  of  iron  ore 
for  the  10  months  ending  Oct.  31  as  $238,972,631  as  compared 
with  imports  for  the  same  period  of  $23,885,776. 

Pig  Iron. — According  to  the  Engineering  and  Mining  Journal 
the  production  the  pig  iron  in  1912  aggregated  29,647,274  tons, 
thereby  surpassing  the  production  of  1910,  and  nearly  equalling 
that  of  1909. 

The  production  is  classified  as  follows : 

Bessemer 11,740,055 

Basic 11,386,176 

Foundry  and  forge 5,965,591 

Charcoal 353,266 

Spiegel  and  ferro 202,186 


Total 29,647,274 

The  pig  iron  industry  in  the  United  States  during  the  present 
century  has  suffered  three  reverses  due  to  disturbed  financial 
conditions.  The  first  came  in  1904  in  which  the  reduction  was 
approximately  2,000,000  tons.  The  second  came  in  1908  with 
a  reduction  of  approximately  10,000,000  tons.  The  third  came 
in  1911  with  a  reduction  of  approximately  3,500,000  tons. 

Germany  stands  next  to  the  United  States  in  the  production 
of  both  pig  iron  and  steel.  The  amount  approximates  13,000,000 
tons  of  each  commodity.  The  United  Kingdom  ranks  third 


ECONOMICS  301 

in  the  list.     The  output  of  pig  iron  approximates  10,000,000 
metric  tons,  and  of  steel  6,000,000  tons. 

The  United  States  produces  nearly  one-half  of  both  the  pig 
iron  and  steel  of  the  world.  The  three  great  nations,  the  United 
States,  Germany,  and  the  United  Kingdom  produce  approxi- 
mately four-fifths  of  the  world's  supply  of  these  two  most 
important  commodities. 

ALUMINUM 

The  increase  in  the  magnitude  of  the  aluminum  industry  in 
the  United  States  is  reflected  by  the  fact  that  in  1883  the  produc- 
tion was  only  83  Ib.  and  in  1911  it  was  46,125,000  Ib.  In  1912 
there  was  no  substantial  increase  in  the  production  of  the 
metal  nor  any  substantial  change  in  the  general  manufacturing 
conditions.  The  Aluminum  Company  of  America  is  at  present 
the  chief  manufacturer  of  the  metal  in  the  United  States. 

There  were  no  radically  new  uses  for  the  metal  developed 
during  the  year.  There  was  marketed  a  new  electrical  conductor 
composed  of  seven  wires.  The  center  wire  was  steel  of  high 
tensile  strength.  This  type  of  cable  supplies  a  conductor  that  is 
both  light  and  strong  for  long  distance  transmission  work. 

A  minor  new  use  for  the  metal  lies  in  the  manufacture  of 
aluminum  foil  which  is  displacing  tin  foil  as  a  wrapper  for  candy 
and  tobacco. 

CHROME  IRON  ORE 

According  to  W.  C.  Phalen  the  production  of  chrome  iron  ore 
in  1911  was  only  120  long  tons  valued  at  $1629.  This,  however, 
represents  the  amount  actually  sold.  It  is  a  reduction  of  almost 
50  per  cent,  in  both  tonnage  and  value  from  that  of  1910. 

The  chrome  iron  industry  has  been  fluctuating  and  is  declin- 
ing. Prices  have  had  a  downward  trend.  This  fact  seems  a  little 
strange  in  the  light  of  the  quotations  for  tungsten  and  vanadium 
ores  as  ingredients  in  special  steel  alloys,  one  of  the  most  impor- 
tant uses  of  a  chromium.  One  reason  for  the  decline  lies  in  the 
wide  distribution  of  chromite  and  the  pockety  character  of  known 
deposits  free  from  impurities. 

The  chrome  iron  ore  of  recent  years  has  been  produced  mainly 
in  New  Caledonia,  Asia  Minor,  Greece,  Canada,  India,  Rhodesia 


302  ECONOMIC  GEOLOGY 

and  Japan.  The  supply  in  New  Caledonia  is  the  best  known  but 
this  also  fluctuates  in  the  amount  and  value  of  its  production. 
In  1906  the  production  of  this  single  field  was  84,241  metric 
tons,  but  in  1907  it  fell  to  3800  metric  tons.  The  output  of  Rus- 
sia where  the  industry  centers  in  the  Urals,  and  in  India  in  Balu- 
chistan and  Mysore,  the  industry  is  subject  to  the  same  fluctua- 
tions. The  output  of  Rhodesia  which  is  the  foremost  producer  at 
present  is  increasing.  The  mines  are  not  far  from  Selukwe, 
about  560  miles  from  the  port  of  Beira.  The  production  from 
Rhodesia  shows  that  ores  from  deposits  in  a  comparatively 
inaccessible  part  of  the  world  may  be  placed  upon  the  European 
market  under  conditions  which  enable  them  to  compete  with 
more  favorably  situated  supplies. 

COBALT 

According  to  F.  L.  Hess  there  was  no  production  of  cobalt  in 
the  United  States  in  1911.  A  possible  source  of  cobalt  lies  in 
the  concentrates  saved  in  extracting  lead  ores  at  Fredericktown 
and  Mine  La  Motte,  Missouri.  A  second  possible  source  when 
transportation  facilities  are  improved  is  near  Blackbird,  Idaho. 
The  supply  of  cobalt  for  domestic  consumption  is  said  to  come 
wholly  from  Cobalt,  Ontario.  The  ores  are  shipped  to  England 
and  the  oxide  imported.  Cobaltiferous  ores  from  which  the 
oxide  is  also  manufactured  are  treated  by  the  Orford  Copper 
Company,  Constable  Hook,  N.  Y. 

The  interesting  alloy  stellite,  composed  of  cobalt  and  chromium, 
is  manufactured  on  a  small  scale  for  knives  with  stellite  blades. 
This  use  appears  to  hold  the  most  promising  outlook  for  the 
metal. 


NICKEL 

A  small  amount  of  nickel,  amounting  approximately  to 
$125,000  is  saved  as  a  by-product  from  the  electrolytes  of  the 
copper  refineries.  Much  of  the  copper  refined  electrolytically 
contains  small  percentages  of  nickel  which  during  the  process  of 
refining  the  copper  passes  into  the  electrolyte.  If  the  accumu- 
lation exceeds  1  per  cent,  it  is  said  to  be  harmful  to  the  perfect 
deposition  of  the  copper.  The  copper  thus  treated  comes  from 
domestic  and  foreign  sources,  but  the  amount  derived  from 


ECONOMICS  303 

each  source  is  unknown.  All  other  nickel  used  for  domestic 
consumption  comes  from  Sudbury,  Ontario. 

In  the  Sudbury  district  nickel  mining  was  active  during  1912 
and  the  production,  the  largest  on  record,  approximately  21,000 
tons.  The  Canadian  Copper  Company  by  a  series  of  testing 
in  the  Frood  mine  is  said  to  have  proven  in  this  mine  alone  the 
existence  of  10,000,000  tons  of  ore. 

The  Mond  Nickel  Company  carried  on  development  work  on 
an  extension  of  the  Frood  ore  body.  The  Alexo  mine  in  Dun- 
donald  township  shipped  several  thousand  tons  of  good  ore  during 
the  latter  part  of  1912  to  the  Mond  Nickel  Company's  smeltery 
at  Victoria  Mines. 

The  Dominion  Nickel-Copper  Company  by  a  similar  series  of 
drill  testings  has  proven  the  existence  of  about  6,000,000  tons  of 
ore  about  one-fourth  mile  west  of  the  old  Murray  mine. 

The  imports  of  nickel  average  about  $4,000,000  while  the 
exports  of  nickel,  nickel  oxide,  and  matte  surpass  $8,000,000. 

MANGANESE 

The  managanese  industry  in  the  United  States  depends 
largely  upon  the  activities  in  the  pig  iron  and  steel  industries. 
With  the  increased  production  of  pig  iron  during  the  last  two 
years  there  has  been  a  greater  demand  for  managnese  ores. 
The  production,  however,  has  been  small,  averaging  about 
2,500  tons  per  year  valued  approximately  at  $25,000.  Virginia 
and  California  are  the  principal  producers.  The  value  of  the 
imports  of  managnese  ores  for  domestic  consumption  exceeds 
$1,000,000. 

The  annual  domestic  production  of  manganiferous  ores  exceeds 
500,000  long  tons.  The  Lake  Superior  region  produced  over 
91  per  cent,  of  the  tonnage.  The  ore  averages  less  than  6  per 
cent,  of  manganese  and  is  used  a  source  of  high-manganese 
pig  iron.  The  manganese  ores  of  Colorado,  which  is  the  second 
state  in  rank  in  this  industry,  are  used  for  fluxing.  These  ores 
are  also  argentiferous.  The  manganiferous  ores  of  Batesville, 
Arkansas,  are  utilized  in  the  manufacture  of  high-manganese 
pig  iron  in  the  blast  furnaces  at  St.  Louis,  Missouri. 

The  production  of  manganese- zinc  residuum  from  New  Jersey 
zinc  ores  has  averaged  more  than  100,000  long  tons  per  annum. 
These  ores  consist  of  franklinite,  zincite,  and  willemite.  In 


304  ECONOMIC  GEOLOGY 

the  roasting  process  most  of  the  zinc  is  removed,  and  the  residuum 
consists  largely  of  manganese  and  iron  oxides.  These  are  .used 
for  the  manufacture  of  ferromanganese  and  spiegeleisen.  The 
largest  value  for  this  product  was  recorded  in  1908,  viz.,  $423,792. 

The  manganese  deposits  of  the  Caucasus  are  among  the  richest 
in  the  world.  The  principal  mines  are  at  Tchiatouri  in  the 
Government  of  Kotais,  about  126  miles  from  the  ports  of  Batum 
and  Poti  on  the  Black  Sea.  England,  Germany,  and  the  United 
States  are  the  largest  purchasers.  Smaller  quantities  are 
shipped  to  France  and  Belgium.  The  total  exports  from  these 
shipping  points  during  the  last  few  years  has  averaged  approxi- 
mately 500,000  tons. 

Manganese  ores  are  mined  in  widely  separated  districts  in 
India.  The  production  now  approximates  1,000,000  metric 
tons  per  annum.  Some  of  the  manganese  mines  in  the  State 
of  Minas  Geraes,  Brazil,  have  been  worked  since  1894,  with 
an  annual  production  of  about  60,000  tons.  In  the  States  of 
Bahia  and  Matto  Grosso  manganese  ores  are  also  mined.  The 
Brazillian  ores  are  estimated  as  sufficient  to  supply  the  world's 
requirements  for  several  centuries. 

ZINC 

The  principal  source  of  zinc  ores  for  1912  came  from  the 
Joplin  district  in  Missouri,  the  Wisconsin  district,  Leadville, 
Colorado,  and  Butte,  Montana.  According  to  C.  E.  Siebenthal 
of  the  United  States  Geological  Survey  the  zinc  industry  for 
1912,  stimulated  by  the  prevailing  high  price  of  spelter,  went 
far  beyond  all  preceding  records  in  the  production  of  spelter. 
The  production  of  primary  spelter  from  domestic  ores  was 
323,961  short  tons  and  from  foreign  ores  14,669  tons  making  a 
total  aggregate  of  338,630  tons.  The  value  of  this  banner  pro- 
duction is  estimated  at  $46,731,000  which  is  an  increase  of  more 
than  $12,000,000  over  the  value  of  the  production  for  1911. 

The  imports  of  zinc  ore  for  1912  were  approximately  78,000 
short  tons,  containing  about  31,500  tons  of  zinc.  This  excludes 
18,245  tons  of  lead  ore  from  South  America  which  contained 
2,431  tons  of  zinc.  This  amount  was  not  recovered  in  the 
smelting  of  the  lead. 

The  imports  of  spelter  for  1912  were  the  largest  for  many  years. 
The  amount  is  estimated  at  10,700  short  tons  and  the  value  at 
$1,202,000. 


ECONOMICS  305 

The  exports  of  domestic  zinc  ores  were  19,953  short  tons  and 
the  export  of  zinc  dross  for  the  same  year  amounted  to  203 
short  tons. 

The  average  price  of  spelter  at  St.  Louis,  Missouri,  was  6.9 
cents  per  pound  as  compared  with  5.7  cents  for  1911. 

The  United  States  ranks  first  as  a  producer  of  spelter  and  is 
closely  followed  by  Germany  and  Belgium.  The  world's 
production  of  spelter  in  1912  was  956,335  metric  tons. 

MOLYBDENUM 

There  is  annually  a  small  production  of  molybdenum  ore  in 
the  United  States.  The  Primos  Chemical  Company  of  Primos, 
Pennsylvania,  is  the  chief  manufacturer  of  molydenum  and 
ferro-molybdenum  in  this  country. 

The  price  of  the  metal  in  1912  was  $1.40  per  pound  and  of 
the  alloy  about  $1 .60  per  pound  of  its  molybdenum  content. 

The  metallurgical  requirement  for  molybdenite  is  92  per 
cent,  molybdenum  sulphide.  The  value  of  such  ore  is  approxi- 
mately $400  per  ton.  To  maintain  this  value  the  ore  must  be 
reasonably  free  from  copper  as  the  latter  is  an  objectionable 
impurity. 

Lower  grade  molybdenite  ores  are  valued  at  about  $1  per  unit. 
This  holds  especially  true  if  the  ore  concentrates  to  25  per  cent, 
molybdenum  sulphide.  Wulfenite  which  contains  25  per  cent, 
of  molybdic  trioxide,  MoOa,  is  worth  about  $100  per  ton. 

TUNGSTEN 

According  to  F.  L.  Hess  of  the  United  States  Geological  Survey 
the  amount  of  tungsten  ores  mined  and  marketed  in  the  United 
States  in  1912  was  1290  tons  carrying  60  per  cent,  tungsten 
trioxide,  WOs.  The  value  of  this  product  was  estimated  at 
$492,000.  It  was  a  substantial  increase  over  the  output  of 
1911.  The  average  price  per  unit  was  $6.35.  The  unit  is  1 
per  cent,  of  a  short  ton  of  tungsten  trioxide. 

The  largest  production  of  any  single  district  came  from  the 
unique  ferberite  deposits  of  Boulder  County,  Colorado.  About 
1200  tons  of  ore  was  shipped  from  this  district.  The  Primos 
Mining  and  Milling  Company  and  the  Wolf  Tongue  Mining 
Company  are  the  largest  producers. 
20 


306  ECONOMIC  GEOLOGY 

In  California  the  Atolia  Mining  Company,  which  controls  the 
Atolia  field  at  the  north  edge  of  San  Bernadino  County,  increased 
its  production  ofscheelite.  This  company  is  the  largest  indi- 
vidual producer  of  tungsten  ores  in  the  United  States. 

A  new  discovery  of  scheelite  was  reported  from  the  west  side 
of  Rand  Mountains  but  no  ore  was  sold  during  1912.  A  few 
tons  of  mixed  scheelite  and  wolframite  were  shipped  from  the 
vicinity  of  Nipton  in  the  east  end  of  San  Bernadino  County. 

In  Arizona  a  few  tons  of  hubnerite  were  shipped  from  the  dry 
placers  and  some  ore  from  the  veins  near  Dragoon.  Hubnerite 
was  shipped  also  from  Arivaca  and  scheelite  from  Oracle.  Other 
small  shipments  were  made  from  Nevada,  Idaho,  Washington, 
and  New  Mexico. 


URANIUM 

The  production  of  uranium  oxide  for  1912  has  been  estimated 
by  F.  L.  Hess  as  26  short  tons.  This  would  represent  approxi- 
mately 20  tons  of  metallic  uranium.  This  was  a  slight  increase 
over  the  production  of  1911. 

The  uraniferous  ores  were  all  carnotite,  a  variable  compound 
of  uranium  and  vanadium,  from  the  Jura-Trias  formations  of 
the  high  plateau  region  of  Colorado  and  Utah.  The  largest  and 
richest  deposits  are  found  in  Montrose  County,  Colorado,  in 
Paradox  Valley,  Long  Park,  and  the  Mclntyre  districts.  In 
Utah  the  carnotite  came  from  Emery  and  Grand  Counties. 

A  small  amount  of  uraninite  was  mined  near  Central  City, 
Gilpin  county,  Colorado,  and  sold  as  laboratory  material.  A 
few  pounds  partly  altered  to  gummite  were  mined  near  Penland, 
North  Carolina. 


VANADIUM 

The  larger  part  of  the  vanadium  ore  mined  in  the  United  States 
in  1912  was  a  sage-green  vanadiferous  sandstone  which  contains 
the  vanadium  mica,  roscoelite.  It  was  mined  near  Newmire, 
San  Miguel  County,  Colorado.  The  vanadium  was  obtained  in 
the  form  of  an  iron  vanadate  at  the  local  reduction  plant  of  the 
Primos  Chemical  Company.  The  iron  vanadate  was  shipped 
east  to  be  smelted  into  ferro-vanadium.  The  price  of  metallic 
vanadium  in  former  years  has  been  from  $4  to  $5  per  pound 


ECONOMICS  307 

but  in  1912  it  fell  to  $2.50  and  $2  for  the  vanadium  contained 
in  ferro-vanadium. 

The  imports  of  roasted  patronite,  a  vanadium  sulphide,  from 
Peru,  were  large  and  the  production  of  ferro-vanadium  probably 
the  largest  in  the  history  of  the  industry. 

TITANIUM 

According  to  F.  L.  Hess  there  was  only  one  American  producer 
of  rutile  in  1912.  This  was  the  American  Rutile  Company  whose 
mine  and  mill  are  located  at  Roseland,  Nelson  County,  Virginia. 
This  company  produced  in  1912,  275  tons  of  concentrates  carry- 
ing from  80  to  85  per  cent.  Ti02.  The  principal  impurity  is  an 
iron  oxide  in  ilmenite.  The  ilmenite  is  separated  from  the  rutile 
by  an  electro  magnet.  About  100  tons  of  concentrates  were 
produced  in  1912,  containing  94  per  cent,  of  Ti(>2.  The  separated 
material  carries  from  50  to  60  per  cent,  of  titanic  oxide  and  42.3 
per  cent,  of  iron  oxide.  The  prices  ranged  from  $30  to  $100 
per  ton  according  to  percentages  of  Ti(>2  and  the  quantity  of 
the  concentrates  placed  at  one  time. 

ZIRCONIUM 

The  production  of  zirconium  in  the  United  States  is  limited  to 
a  few  thousand  pounds  per  annum.  In  1910  there  was  no  output 
recorded.  The  product  is  generally  derived  from  the  monazite 
sands  of  North  Carolina.  Another  interesting  locality  is  Barin- 
ger  Hill,  Texas.  This  locality  is  12  miles  north  of  Kingsland,  the 
nearest  railroad  station. 

The  economic  interest  in  the  rare  earth  minerals  centers  in 
their  incandescence  when  heated.  Thoria,  beryllia,  yttria,  and 
zirconia  show  this  property  in  the  largest  degree.  Thoria  and 
beryllia  form  the  bulk  of  the  incandescent  oxides  used  in  gas  man- 
tles. They  are  too  easily  volatilized  to  be  used  in  an  electric 
glower,  such  as  the  Nernst  lamp.  Zirconia  and  yttria  will  stand 
the  necessary  high  temperature. 

According  to  the  January-March,  1913,  Bulletin  of  the  Impe- 
rial Institute  the  largest  use  of  zirconia  lies  in  its  employment 
as  a  refractory  material.  Crucibles  moulded  from  a  mixture  of 
90  parts  of  zirconia  and  10  parts  of  magnesia  made  into  a  paste 
with  10  per  cent,  of  phosphoric  acid  are  extremely  resistant  to 


308  ECONOMIC  GEOLOGY 

heat  and  practically  unaffected  by  molten  alkalis  and  strong 
acids.  Starch  is  sometimes  used  as  a  binder.  The  crucibles  are 
dried  for  several  days  and  fired  in  a  Hempel  electric  furnace  at  a 
temperature  of  2000  to  3000°  C. 

Owing  to  the  low  coefficient  of  expansion  of  zirconia  these  wares 
can  be  plunged  red-hot  into  water  without  risk  of  fracture. 

A  small  amount  of  zirconium  is  manufactured  into  ferro-zircon- 
ium  which  is  used  in  the  refining  of  steel. 

COLUMBIUM 

The  production  of  columbite  in  the  United  States  is  limited  to 
the  mining  of  a  few  hundred  pounds  annually  for  museum  and 
laboratory  material.  Such  a  production  was  produced  in  1911 
by  E.  E.  Hesnard,  Custer,  South  Dakota. 

TANTALUM 

The  production  of  tantalum  in  the  United  States  is  likewise 
small.  It  is  derived  largely  for  domestic  consumption  from  the 
mineral  tantalite.  The  one  use  which  has  brought  tantalum 
into  prominence  has  been  the  making  of  filaments  for  incandes- 
cent electric  lamps.  The  toughness  of  the  metal  made  its  use 
popular.  Within  the  last  few  years  the  process  by  which  tungsten 
wires  can  be  drawn  has  been  so  far  improved  that  tantalum  lamps 
can  show  little  advantage  in  toughness  over  tungsten  lamps. 

As  wire  for  incandescent  electric  lamps  tantalum  is  valued  at 
approximately  $500  per  avoirdupois  pound. 

A  small  quantity  of  tantalum  is  annually  imported. 

SELENIUM 

The  production  of  selenium  in  the  United  States  is  not  large. 
It  now  averages  about  10,000  Ib.  The  product  is  obtained  as  a 
by-product  in  the  electrolytic  refining  of  copper.  The  price 
ranges  from  $3  to  $5  per  pound.  Selenium  is  used  in  the  manufac- 
ture of  enamels,  glazes  and  red  glass. 

TELLURIUM 

The  actual  production  of  tellurium  in  the  United  States  is 
small.  It  can  be  recovered  in  considerable  quantities  in  the  elec- 


ECONOMICS  309 

trolytic  refining  of  copper.  It  is  abundant  in  the  Cripple  Creek, 
Colorado,  district  as  the  mineral  calaverite.  It  occurs  also  in  the 
gold  ores  of  the  Camp  Bird  and  Torpedo-Eclipse  Mining  Compa- 
nies in  the  San  Juan  district.  In  the  Cripple  Creek  district 
alone  more  than  500  tons  of  tellurium  has  become  a  waste  prod- 
uct. No  practical  use  is  known  for  the  element  and  therefore 
there  is  no  market.  It  is  known  however  that  in  certain  experi- 
ments the  element  has  shown  a  peculiar  behavior  toward  elec- 
tricity which  seems  to  indicate  that  electrical  uses  may  yet  be 
found  for  tellurium. 


INDEX 


Alabandite,  246 
Alaska,  77,  78,  155 
Allemontite,  164 
Altaite,  285 
Aluminite,  228 
Aluminum,  218 

character  of  ore  bodies,  221 

extraction  of,  225 

geographical  distribution,  222 

geological  horizon,  225 

ores  of,  218 

origin  of  ores,  219 

production  of,  301 

properties  of,  218 

uses  of,  225 
Alunite,  218 
Alunogen,  218 
Amalgam,  126 
Amalgamation,  86,  98 
Amonal,  227 
Andrews,  T.,  190 
Anglesite,  110,  111 
Annabergite,  238 
Antimonial  lead,  175 
Antimony,  171 

character  of  ore  bodies,  172 

extraction  of,  173 

for  domestic  consumption,  176 

geographical  distribution,  172 

geological  horizon,  173 

ores  of,  171 

origin  of  ores,  171 

production  of,  298 

properties  of,  171 

uses  of,  174 
Argentite,  90 
Arsenic,  164 

character  of  ore  bodies,  165 

extraction  of,  167 

geographical  distribution,  165 


Arsenic,  geological  horizon,  167 

in  alloys,  170 

ores  of,  164 

origin  of  ores,  164 

production  of,  297 

properties  of,  164 

sources  of,  167 

uses  of,  297 
Arsenolite,  164 
Arsenopyrite,  164 
Arsenuretted  hydrogen,  167 
Asbolite,  235 

Ashcroft  and  Swinburne,  265 
Aspen,  Colorado,  95 
Atacamite,  135  t 

Awaruite,  238 
Azurite,  135 


B 


Babbitt,  174 
Bahia,  Brazil,  252,  252 
Barlow,  A.  E.,  239 
Batesville,  Arkansas,  251 
Baux,  France,  224 
Bauxite,  218,  224,  229 

metasomatic,  40 
Bayley,  W.  S.,  207,  209 
Beccarite,  275 
Beck,  R.,  136 
Becker,  G.  F.,  165 
Bell,  R.,  39 

metal,  185 
Belonesite,  268 
Berzelianite,  283 
Beyrichtite,  238 
Bingham,  Utah,  154 
Birmingham,  Alabama,  200 
Bisbee,  Arizona,  150 
Bischof,  G.,  2 
Bismite,  131 
Bismuth,  131 
311 


312 


INDEX 


Bismuth,  character  of  ore  bodies,  132 

extraction  of,  133 

geographical  distribution,  132 

geological  horizon,  132 

native,  131 

ores  of,  131 

origin  of  ores,  131 

production  of,  294 

properties  of,  131 

uses  of,  133 
Bismuthinite,  131 
Bismutite,  131 
Bismutosphaerite,  131 
Black  Hills,  South  Dakota,  62,  180 
Blue  lead,  125 
Bolivia,  183 
Bornite,  135 
Boussingault,  J.  B.,  247 
Boutwell,  J.  M.,  155 
Braddelyite,  275 
Branner,  J.  C.,  224 
Braunite,  246 
Brochantite,  135 
Broggerite,  279 
Bromyrite,  90 
Brookite,  273 
Browne,  D.  H.,  239 
Burchard,  E.  F.,  299 
Butler,  B.  S.,  296 
Butte,  Montana,  91,  146 


Cadmium,  161 

character  of  ores,  162 

extraction  of,  162 

geographical  distribution,  162 

geological  horizon,  162 

ores  of,  162 

origin  of  ores,  162 

production  of,  296 

properties  of,  161 

uses  of,  162 
Calamine,  257 
Calaverite,  52,  285 
Calomel,  126 

Campbell,  Wm.,  97,  192,  239 
Carnelly,  T.,  136 
Carnotite,  276,  279 


Cassiterite,  31,  177 
Cavities,  origin  of,  7,  8,  9 
Ceboela  district,  Colorado,  210 
Cerargyrite,  90 
Cerussite,  110 
Cervantite,  171 
Chalcanthite,  135 
Chalcocite,  135 
Chalcopyrite,  135,  136 
Challenger  expedition,  24 
Chamberlain,  T.  C.,  24 
Chloanthite,  238 
Chrome  ocher,  230 
Chromite,  232,  236 
Chromium,  230 

character  of  ore  bodies,  231 

extraction  of,  231 

geographical  distribution,  231 

ores  of,  230 

origin  of  ores,  230 

production  of,  301 

properties  of,  230 

uses  of,  231 
Chrysocolla,  135 
Cinnabar,  126,  127 
Clarke,  F.  W.,  43,  91,  132,  138,  164, 
171,    177,    178,    190,    191, 
194,    219,    236,    238,    246, 
247,  257,  272,  275 
Clarke,  J.  M.,  198 
Clausthalite,  283 
Clements,  J.  M.,  206,  209 
Cleveite,  279 

Clifton-Morenci  district,  152 
Clinton,  New  York,  190,  200 
Cobalt,  235 

character  of  ore  bodies,  235 

extraction  of,  237 

geographical  distribution,  236 

geological  horizon,  237 

ores  of,  235 

origin  of  ore  bodies,  235 

production  of,  302 

properties  of,  235 

uses  of,  237 
Cobaltite,  237 
Cobalt,  Ontario,  97,  237 
Coeur  d'Alene,  Idaho,  95 
Coleman,  A.  P.,  192,  239 


INDEX 


313 


Collins,  J.  H.,  177 
Coloradoite,  285 
Columbite,  281 
Columbium,  281 

character  of  ore  bodies,  281 

extraction  of,  281 

geographical  distribution,  281 

geological  horizon,  281 

production  of,  308 

properties  of,  281 

uses  of,  281 

Comstock  Lode,  Nevada,  72,  95 
Cook,  G.  H.,  190 
Coolgardite,  53 
Copper,  135 

character  of  ore  bodies,  139 

chlorination  process,  158 

electrolytic  process,  158 
«        extraction  of,  157 

geographical  distribution,  140 

geological  horizon,  157 

in  Vermont,  141 

native,  135 

ores  of,  135 

metasomatic,  40 
primary,  35 

origin  of  ores,  136 

oxidation  process,  158 

production  of,  295 

properties  of,  135 

reduction  process,  157 

scrap  iron  process,  158 

uses  of,  159 

Copperfield,  Vermont,  142,  143 
Copper  River  district,  157 
Coquimbite,  189. 
Coracite,  279 

Cornwall,  England,  32,  177,  181 
Corundum,  218,  221 
Cotunnite,  110 
Covellite,  135 

Cripple  Creek,  Colorado,  66 
Crocoite,  110,  230 
Crook,  A.  R.,  268 
Crookesite,  283 
Cryolite,  218,  222,  229 
Crystal  Falls  district,  209 
Cuprite,  135 
Cuprodescloizite,  276 


Cuprotungstite,  269 
Cuyuna  district,  207 
Cyanide  process  for  gold,  87 
for  silver,  101 


Dana,  J.  D.,  138,  172 
DaubrSe,  A.,  165,  190,  191 
DaubrSelite,  230 
Deep  Creek,  Utah,  46 
Derby,  O.  A.,  248 
Descloizite,  276 
Detrital  deposits,  47 
Diaspore,  218 
Dieulafait,  L.,  246,  257 
Dioptase,  135 
Dip,  9 

Doelter,  C.,  177 
Doherty,  W.  M.,  248 
Dolomitization,  7 

E 

Eckel,  E.  C.,  201 

Elba,  Island  of,  214 

Embolite,  90 

Emery,  218 

Emmons,  S.  F.,  94,  117,  118 

Enargite,  135 

Erythrite,  235 

Eucairite,  283 

Euxenite,  281 


Fay,  A.  H.,  181 

Faults,  9 

Federated  Malay  States,  181 

Fergusonite,  281 

Ferrochrome  alloy,  233 

Ferromanganese,  255 

Foot  wall,  12 

Forschammer,  G.,  246 

Franklin  Furnace,  New  Jersey,  250, 

259 

Franklinite,  190,  257 
Freiberg  district,  97 


314 


INDEX 


G 


Gangue,  1 

Garnierite,  238 

Gautier,  A.,  165 

Geikie,  A.,  194 

Genth,  F.  A.,  178 

Genthite,  238 

Georgia-Alabama  district,  223 

Georgetown  district,  Colorado,  70 

Gersdorffite,  238 

Gibbsite,  212,  222 

Globe,  Arizona,  152 

Gold,  33 

chlorination  process,  88 

cyanide  process,  87 

deposits,    classification   of,    58, 

59,60 
metasomatic,  40 

detrital,  49 

electrolytic  process,  88 

extraction  of,  86,  87,  88 

geographical  distribution,  60 

geological  horizon,  83 

occurrence  of,  52 

ores  of,  52 

origin  of  ores,  53 

placer  mining,  84 

primary  veins,  34 

production  of,  287 

properties  of,  52 

sodium  thiosulphate  process,  88 

uses  of,  89 

Goldfield,  Nevada,  72 
Goslarite,  257 
Gossan,  4,  5 
Gothite,  190,  193 
Gowganda,  Ontario,  97 
Graton,  L.  C.,  179 
Greenockite,  162 
Greisenization,  170 
Griilingite,  286 
Guanajuatite,  131,  283 
Gumbel,  C.  W.,  247 
Gummite,  259 


H 


Hade,  9 
Hague,  A.,  72 


Hall,  James,  201 

Hancock,  E.  T.,  62,  117,  154,  208, 

261 

Hanging  wall,  12 
Hanover,  New  Mexico,  212 
Hausmannite,  246 
Hawes,  G.  W.,  190 
Haworth,  E.,  136 
Hayes,  C.  W.,  219,  223,  224 
Hematite,  190,  195 
Hess,  F.  L.,  181,  270,  273,  282,  295 
Hessite,  52,  90,  285 
Hobart,  F.,  289 
Homestake  district,  62,  63,  64 
Hornstein,  F.  F.,  190 
Horse,  15,  16 
Hiibnerite,  269 
Hussak,  E.,  190 
Hydatogenesis,  33 
Hydrozincite,  257 


Iddings,  J.  P.,  72 

Igneous  rocks,  composition  of,  3 

Ilmenite,  273 

Ilmenorutile,  273 

lodyrite,  90 

lola,  Kansas,  265 

Iridium,  106 

Iridosmine,  107 

Iron,  188 

Appalachian  belt,  197 
character  of  ore  bodies,  195 
classes  of  minerals,  189 
extraction  of,  215 
geographical  distribution,  196 
geological  horizon,  205 
impurities  in,  196 
metasomatic  deposits,  38,  201 
native,  189 

ores  and  minerals,  189 
origin  of  ores,  190 
precipitated  deposits,  41 
production  of,  300 
properties  of,  188 
residual  enrichment,  201 
sedimentary  origin,  201 
uses  of,  216 


INDEX 


315 


Iron  Mountain,  Wyoming,  212 
Irving,  J.  D.,  64,  270 
Irving,  R.  D.,  209 


Jaipurite,  235 

Jenney,  W.  P.,  258 

Jerome  district,  Arizona,  152 

Joplin,  Missouri,  260,  267 

Joseite,  285 

Josephinite,  238 


K 


Kalgoorlite,  53 

Kemp,  J.  F.,  190,  260 

Kermesite,  171 

Keyes,  C.  R.,  1,  24,  240,  258 

King,  Clarence,  72 

Klondike,  Yukon  Territory,  80, 81, 84 

Knight,  C.  W.,  239 

Kotsina  district,  Alaska,  157 

Krennerite,  52,  285 


Lake  Superior  region,  142 

Lane,  A.  C.,  136,  142,  144,  145 

Laterite,  49 

Laurite,  103 

Lead,  110 

character  of  ore  bodies,  111 
extraction  of,  122 
geographical  distribution,  114 
geological  horizon,  122 
lime-roasting  process,  123 
metasomatic  deposits,  40 
ores  of,  110 
origin  of  ores,  111 
precipitation  process,  127 
primary  ores,  35 
production  of,  292 
properties  of,  110 
reduction  process,  122 
roast-reaction  process,  122 
uses  of,  123 

Leadville,  Colorado,  91,  117 

Leadville  minerals,  94 

Le  Conte,  Joseph,  35 


Lehrbachite,  283 
Leucopyrite,  164 
Leucoxane,  272 
Lieth,  C.  K.,  192,  204 
Limonite,  190,  193 

gossan,  204 

residual,  202 
Lindgren,  W.,  77,  136 
Linnaeite,  235 
Lithopone,  267 
Livingstonite,  267 
Lixiviation,  100 
Lollingite,  164 

Losses  of  precious  metals,  108,  109 
Lotti,  B.,  137 


M 


MacAlister.    See  Thomas  and  Mac- 

Alister,  30,  etc. 
Magnalium,  228 
Magnetite,  190,  192,  195 
Malachite,  135 
Mallet,  F.  R.,  248 
Manganese,  245 

character  of  ore  bodies,  248 

extraction  of,  254 

geographical  distribution,  250 

geological  horizon,  254 

precipitated  ores,  41 

production  of,  303 

properties  of,  245 

ores  of,  246 
origin  of,  246 

uses  of,  254 
Manganite,  246 
Manganocolumbite,  281 
Manganosite,  281 
Marcasite,  189 
Marquette  district,  207 
Massicot,  110 
Maumene1,  E.,  246 
McCallie,  S.  W.,  201 
McCasky,  D.  EL,  287 
Menominee  district,  209 
Mercur,  Utah,  26 
Mercury,  126 

character  of  ore  bodies,  127 

distillation  of,  129 


316 


INDEX 


Mercury,  extraction  of,  129 

geographical  distribution,  128 

geological  horizon,  130 

native,  126,  127 

ores  of,  126 

origin  of  ores,  126,  127 

production  of,  293 

properties  of,  126 

roasting  process,  129 

sublimation  of,  129 

uses  of,  130 
Mesabi  Range,  204 
Metamorphism,  42 
Metasamosis,  35 
Meteorites,  content  of,  25 

number  of,  24 
Meunier,  S.,  177,  190,  230 
Michel,  L.,  138 
Miller,  W.  G.,  236,  240 
Minckin,  244 
Mine,  definition  of,  20 
Mineralizers,  30,  33,  40 
Mineral  springs,  6 
Mineville,  New  York,  198 
Minium,  110 

Mississippi  River  belt,  115 
Molybdenum,  268 

character  of  ore  bodies,  268 

extraction  of,  269 

geographical  distribution,  269 

geological  horizon,  269 

ores  of,  268 

origin  of  ores,  268 

production  of,  305 

properties  of,  268 

uses  of,  269 
Molybdic  ocher,  268 
Morenosite,  241 
Morozewicz,  J.,  219 
Mother  Lode,  California,  75 
Mottramite,  276 
Murray,  J.,  247 


N 


Nagyagite,  52 
Nantokite,  135 
Naumannite,  283 
Navarro,  F.,  190 


Newberry  and  Le  Conte,  119 
Niccolite,  164 
Nickel,  238 

character  of  ore  bodies,  241 

extraction  of,  244 

geographical  distribution,  242 

geological  horizon,  243 

ores  of,  238 

origin  of  ores,  238 

production  of,  302 

properties  of,  238 

uses  of,  244 
Nickeloid,  244 
Nigrine,  273 
Nivenite,  279 

Nordenskiold,  A.  E.,  24,  190 
Nordenskioldine,  177 
Noumea,  New  Caledonia,  241 


O 


Octahedrite,  273 

Omichen,  H.,  137 

Orange  mineral,  125 

Ore  bodies,  enrichment  of,  3,  6 

Ore  deposits,  1 

classification  of,  18 

of  Crosby,  18 

of  Kemp,  18 

of  Prosepny,  18 

of  Weed,  18,  19,  20 
meteoric  origin,  24 
Ores,  primary  source  of,  1,  2 
Orpiment,  164,  168 
Osmiridium,  102 
Osmium,  106 
Ouray  district,  Colorado,  69 


Pacific  Coast  region,  75,  153 
Palladium,  106 
Paris  green,  169 
Pateraite,  269 

Pattinson  process,  lead  and  silver,  99 
Peary,  R.  E.,  190 
Penokee-Gogebic  district,  209 
Penrose,  R.  A.  F.,  194,  250 
Pentlandite,  238 


INDEX 


317 


Perovskite,  273 

Peters,  E.  D.,  159 

Petzite,  52,  90,  285 

Pewter  ware,  185 

Pirsson,  L.  V.,  165 

Pitchblende,  279 

Placer  mining,  84,  85,  86,  101 

Placers,  79,  80,  81 

ancient  beach,  81 

associated  minerals,  50,  57 

bench,  81 

creek,  80,  81 

deep  lead,  50 

gravel-plain,  81 

gulch,  80 

hillside,  81 

residual,  80 

river-bar,  81 

sea-beach,  81 

shoad,  50 

sorted,  80 
Platinum,  102 

alloys  of,  105 

character  of  ore  bodies,  102 

detrital,  50 

extraction  of,  104 

geographical  distribution,  103 

geological  horizon,  103 

native,  102 

ores  of,  102 

origin  of  ores,  102 

production  of,  291 

properties  of,  102 

uses  of,  104 
Platiniridium,  102 
Pneumatolysis,  29,  30 
Polianite,  246 
Polybasite,  90 
Polydimite,  238 
Porcupine,  Ontario,  83 
Powellite,  269 
Pratt,  J.  H.,  219,  231 
Precipitation,  41 

causes  of,  4 
Proustite,  90 
Psilomelane,  246 
Pucherite,  276  | 
Pyrargyrite,  90 
Pyrite,  189 


Pyrochlore,  281 
Pyrochroite,  246 
Pyrolusite,  246 
Pyromorphite,  110 
Pyrrhotite,  189,  238 


Quartz,  as  gangue,  1 
Quebec,  Canada,  199,  230 
Queluz,  Brazil,  248 

R 

Rammelsbergite,  238 

Ransome,  F.  L.,  69,  122 

Realgar,  164,  168 

Red  lead,  125 

Reinite,  269 

Rhodium,  107 

Rhodochrosite,  246 

Rhodonite,  246 

Richthofen,  F.,  75 

Rickard,  T.  A.,  80 

Rickardite,  285 

Ries,  Heinrich,  69,  119,  128,  132, 
142,  148,  152,  165,  179, 
200,224,231,242,248,250 

Robertson,  J.  D.,  258 

Roscoelite,  276 

Ruby,  218,  222 

Russell,  I.  C.,  201 

Ruthenium,  107 

Rutile,  272 

S 

Safflorite,  235 

Samarskite,  281 

San  Juan  district,  Colorado,  68 

Sapphire,  218 

Saucon  Valley,  Pennsylvania,  259 

Scheelite,  269 

Schmidt's  law,  11 

Schrivenor,  J.  B.,  183 

Secondary  changes,  46 

Segregation,  25 

causes  of,  26 

order  of,  26 
Selenium,  283 

character  of  ore  bodies,  284 


318 


INDEX 


Selenium,  extraction  of,  284 

geographical  distribution,  284 

geological  horizon,  284 

ores  of,  283 

origin  of  ores,  283 

production  of,  308 

properties  of,  283 

uses  of,  284 
Selen-sulphur,  283 
Selen-tellurium,  283 
Selvage,  12 
Semmons,  W.,  178 
Senarmontite,  171 
Shaler,  N.  S.,  194 
Siderite,  189,  196 
Siebenthal,  C.  E.,  296 
Sierra  region,  72 
Silver,  89 

character  of  ore  bodies,  91 

cyanide  process,  101 

electrolytic  process,  101 

extraction  of,  98 

geographical  distribution,  97 

geological  horizon,  98 

lixiviation  process,  100 

native,  89 

ores  of,  90 

origin  of  ores,  91 

primary  ores,  35 

production  of,  290 

properties  of,  89 

smelting  process,  99 

uses  of,  102 

Silverton  district,  Colorado,  69 
Singewald,  J.  T.,  210 
Sippylite,  281 
Skutterudite,  235 
Smaltite,  164,  235 
Smith,  G.  O.,  268 
Smith,  W.  S.  T.,  262 
Smithsonite,  257 
Smyth,  C.  H.,  183,  201 
Smyth,  H.  L.,  207,  209 
Solder,  185 
Solfataras,  7 
Solutions,  ascending,  2 

descending,  2 

lateral  secreting,  2 

trend  of,  2 


South  Lorrain,  Ontario,  97 
Spencer,  A.  C.,  79,  259,  260 
Sperrylite,  102 
Sphalerite,  257 
Spiegeleisen,  255 
Spurr,  J.  E.,  54,  70,  120 
Stannite,  177 
Steel,  Bessemer,  216 
Stephanite,  90 
Stibnite,  170 
Strike,  9 

Stolzite,  110,  269 
Sudbury,  Ontario,  239 
Swinburne.     See  Ashcroft  and  Swin- 
burne, 265 


Tantalum,  282 

character  of  ore  bodies,  282 

extraction  of,  282 

geographical  distribution,  282 

geological  horizon,  282 

ores  of,  282 

origin  of  ores,  282 

production  of,  308 

properties  of,  282 

uses  of,  282 
Tellurium,  285 

character  of  ore  bodies,  286 

extraction  of,  286 

geographical  distribution,  286 

geological  horizon,  286 

ores  of,  285 

origin  of  ores,  285 

production  of,  308 

properties  of,  285 

uses  of,  286 

Telluride  district,  Colorado,  69 
Tellurite,  286 
Tennantite,  135 
Tenorite,  135 
Tetradymite,  131,  286 
Tetrahedrite,  135 
Thames  district,  95 
Thermit,  227 

Thomas  and  MacAlister,  30,  32,  39, 
112,  137,  140,  167,  172, 
178,  181,  214,  225,  232, 
264 


INDEX 


319 


Thresh,  M.,  248 
Throw,  9 
Tiemannite,  126 
Tin,  176 

character  of  ore  bodies,  178 

extraction  of,  184 

geographical  distribution,  178 

geological  horizon,  184 

in  Alaska,  181 

in  canned  goods,  186 

in  foreign  countries,  181 

ores  of,  177 

origin  of  ores,  177 

production  of,  298 

properties  of,  176 

uses  of,  185 
Titanite,  273 
Titanium,  271 

character  of  ore  bodies,  273 

extraction  of,  274 

geographical  distribution,  274 

geological  horizon,  274 

ores  of,  272,  273 

origin  of  ores,  273 

production  of,  307 

properties  of,  271 

uses  of,  274 
Travertine,  6 
Troy,  Vermont,  199 
Tungsten,  269 

character  of  ore  bodies,  270 

extraction  of,  270 

geographical  distribution,  270 

geological  horizon,  270 

production  of,  307 

properties  of,  269 

uses  of,  270 
Tungstite,  269 
Turgite,  190 
Turquoise,  218 
Type  metal,  174 


U 


Ural  Mountains,  214 
Uraninite,  278 
Uranium,  278 

character  of  ore  bodies,  279 

extraction  of,  280 


Uranium,  geographical  distribution, 
280 

geological  horizon,  280 

ores  of,  279 

origin  of  ores,  279 

production  of,  306 

properties  of,  278 

uses  of,  280 
Utah,  silver  in,  95 


Valentinite,  171 
Vanadium,  276 

character  of  ore  bodies,  277 

geographical  distribution,  277 

geological  horizon,  277 

ores  of,  276 

origin  of  ores,  276 

production  of,  306 

properties  of,  276 

uses  of,  277 

Van  Hise,  C.  R.,  55,  207,  209 
Veatch,  A.  C.,  222 
Veins,  11 

age  of,  18 

fissure,  12 

gash,  12 

irregularities  in,  15,  17 

occurrence  of,  13 

parallel,  13 

ribbon  structure  in,  17 

richness  of,  14 

segregated,  12 
Vermillion,  district,  206 
Vogt,  J.  H.  L.,  28,  46,  191,  239 
Voit,  F.  W.,  240 
Voltzite,  257 


W 


Wad,  246 
Walker,  T.  L.,  239 
Waters,  acidulated,  6 

carbonated,  6 

sulphur  bearing,  7 

thermal,  7,  30 
Watson,  T.  L.,  250 
Weed,  W.  H.,  18,  95, 120, 150,  165 


320 


INDEX 


Wehrlite,  286 
Wells,  J.  W.,  269 
Wheeler,  H.  A.,  258 
White  lead,  124 
Willemite,  257,  258 
Williams,  J.  F.,  224 
Wirthle,  F,.  186 
Wohler,  F,.  225 
Wolff,  J.  E.,  260 
Wolframite,  110,  268 
Wurtzite,  257 

X 

Xanthosiderite,  190 
Y 

Yamada,  K,  173 
Yeats,  W.  S.,  136 
Young,  C.  A.,  24,  191 


Zinc,  256 

character  of  ore  bodies,  259 


Zinc,  extraction  of,  265 

geographical  distribution,  259 

geological  horizon,  264 

metasomatic  deposits,  40 

ores  of,  257 

origin  of  ores,  257 

primary  ores,  35 

production  of,  304 

properties  of,  256 

uses  of,  266 
Zincite,  257 
Zircon,  275 

Zirconia,  North  Carolina,  276 
Zirconium,  274 

character  of  ore  bodies,  275 

extraction  of,  275 

geographical  distribution,  275 

geological  horizon,  275 

ores  of,  275 

origin  of  ores,  275 

production  of,  307 

uses  of,  276 
Zorgite,  283 


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